feat: Start using Firefox's split views to prevent memory leaks, b=no-bug, c=common, split-view

src/browser/components/tabbrowser/AsyncTabSwitcher-sys-mjs.patch

@@ -1,12 +1,12 @@
 diff --git a/browser/components/tabbrowser/AsyncTabSwitcher.sys.mjs b/browser/components/tabbrowser/AsyncTabSwitcher.sys.mjs
-index bcd7689e9d68ef8b171c327188174334c4271e21..f69180acb87644f109aa91b871e347f1b1835f53 100644
+index bcd7689e9d68ef8b171c327188174334c4271e21..0a95e1137fdf4b63e0d841776ad934da1a513c6f 100644
 --- a/browser/components/tabbrowser/AsyncTabSwitcher.sys.mjs
 +++ b/browser/components/tabbrowser/AsyncTabSwitcher.sys.mjs
 @@ -938,6 +938,7 @@ export class AsyncTabSwitcher {
        this.tabbrowser._printPreviewBrowsers.has(browser) ||
        this.tabbrowser.splitViewBrowsers.includes(browser) ||
        lazy.PictureInPicture.isOriginatingBrowser(browser)
-+      || browser?.parentNode?.parentNode?.parentNode?.classList?.contains("zen-glance-background")
++      || browser?.zenModeActive
      );
    }
  

src/browser/components/tabbrowser/content/tabbrowser-js.patch

@@ -1,8 +1,16 @@
 diff --git a/browser/components/tabbrowser/content/tabbrowser.js b/browser/components/tabbrowser/content/tabbrowser.js
-index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326cbd973686 100644
+index c0eafd4faf8d57b8486c5bf8917375850ec8147e..cead9e6e52f7354e20b8b64ad06a075e6923fe5f 100644
 --- a/browser/components/tabbrowser/content/tabbrowser.js
 +++ b/browser/components/tabbrowser/content/tabbrowser.js
-@@ -450,15 +450,64 @@
+@@ -386,6 +386,7 @@
+      * @type {MozBrowser[]}
+      */
+     get splitViewBrowsers() {
++      return gZenViewSplitter.splitViewBrowsers;
+       const browsers = [];
+       if (this.#activeSplitView) {
+         for (const tab of this.#activeSplitView.tabs) {
+@@ -450,15 +451,64 @@
        return this.tabContainer.visibleTabs;
      }
  
@@ -69,7 +77,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
      set selectedTab(val) {
        if (
          gSharedTabWarning.willShowSharedTabWarning(val) ||
-@@ -613,6 +662,7 @@
+@@ -613,6 +663,7 @@
        this.tabpanels.appendChild(panel);
  
        let tab = this.tabs[0];
@@ -77,7 +85,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        tab.linkedPanel = uniqueId;
        this._selectedTab = tab;
        this._selectedBrowser = browser;
-@@ -898,13 +948,17 @@
+@@ -898,13 +949,17 @@
        }
  
        this.showTab(aTab);
@@ -96,7 +104,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
  
        aTab.setAttribute("pinned", "true");
        this._updateTabBarForPinnedTabs();
-@@ -917,11 +971,15 @@
+@@ -917,11 +972,15 @@
        }
  
        this.#handleTabMove(aTab, () => {
@@ -113,7 +121,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        });
  
        aTab.style.marginInlineStart = "";
-@@ -1098,6 +1156,8 @@
+@@ -1098,6 +1157,8 @@
  
        let LOCAL_PROTOCOLS = ["chrome:", "about:", "resource:", "data:"];
  
@@ -122,7 +130,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        if (
          aIconURL &&
          !LOCAL_PROTOCOLS.some(protocol => aIconURL.startsWith(protocol))
-@@ -1107,6 +1167,9 @@
+@@ -1107,6 +1168,9 @@
          );
          return;
        }
@@ -132,7 +140,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
  
        let browser = this.getBrowserForTab(aTab);
        browser.mIconURL = aIconURL;
-@@ -1379,7 +1442,6 @@
+@@ -1379,7 +1443,6 @@
  
        // Preview mode should not reset the owner
        if (!this._previewMode && !oldTab.selected) {
@@ -140,7 +148,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        }
  
        let lastRelatedTab = this._lastRelatedTabMap.get(oldTab);
-@@ -1470,6 +1532,7 @@
+@@ -1470,6 +1533,7 @@
        if (!this._previewMode) {
          newTab.recordTimeFromUnloadToReload();
          newTab.updateLastAccessed();
@@ -148,7 +156,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          oldTab.updateLastAccessed();
          // if this is the foreground window, update the last-seen timestamps.
          if (this.ownerGlobal == BrowserWindowTracker.getTopWindow()) {
-@@ -1622,6 +1685,9 @@
+@@ -1622,6 +1686,9 @@
        }
  
        let activeEl = document.activeElement;
@@ -158,7 +166,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        // If focus is on the old tab, move it to the new tab.
        if (activeEl == oldTab) {
          newTab.focus();
-@@ -1945,7 +2011,8 @@
+@@ -1945,7 +2012,8 @@
      }
  
      _setTabLabel(aTab, aLabel, { beforeTabOpen, isContentTitle, isURL } = {}) {
@@ -168,7 +176,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          return false;
        }
  
-@@ -2053,7 +2120,7 @@
+@@ -2053,7 +2121,7 @@
          newIndex = this.selectedTab._tPos + 1;
        }
  
@@ -177,7 +185,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          if (this.isTabGroupLabel(targetTab)) {
            throw new Error(
              "Replacing a tab group label with a tab is not supported"
-@@ -2328,6 +2395,7 @@
+@@ -2328,6 +2396,7 @@
        uriIsAboutBlank,
        userContextId,
        skipLoad,
@@ -185,7 +193,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
      } = {}) {
        let b = document.createXULElement("browser");
        // Use the JSM global to create the permanentKey, so that if the
-@@ -2401,8 +2469,7 @@
+@@ -2401,8 +2470,7 @@
          // we use a different attribute name for this?
          b.setAttribute("name", name);
        }
@@ -195,7 +203,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          b.setAttribute("transparent", "true");
        }
  
-@@ -2567,7 +2634,7 @@
+@@ -2567,7 +2635,7 @@
  
        let panel = this.getPanel(browser);
        let uniqueId = this._generateUniquePanelID();
@@ -204,7 +212,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        aTab.linkedPanel = uniqueId;
  
        // Inject the <browser> into the DOM if necessary.
-@@ -2626,8 +2693,8 @@
+@@ -2626,8 +2694,8 @@
        // If we transitioned from one browser to two browsers, we need to set
        // hasSiblings=false on both the existing browser and the new browser.
        if (this.tabs.length == 2) {
@@ -215,7 +223,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        } else {
          aTab.linkedBrowser.browsingContext.hasSiblings = this.tabs.length > 1;
        }
-@@ -2814,7 +2881,6 @@
+@@ -2814,7 +2882,6 @@
              this.selectedTab = this.addTrustedTab(BROWSER_NEW_TAB_URL, {
                tabIndex: tab._tPos + 1,
                userContextId: tab.userContextId,
@@ -223,7 +231,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
                focusUrlBar: true,
              });
              resolve(this.selectedBrowser);
-@@ -2923,6 +2989,8 @@
+@@ -2923,6 +2990,8 @@
          schemelessInput,
          hasValidUserGestureActivation = false,
          textDirectiveUserActivation = false,
@@ -232,7 +240,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        } = {}
      ) {
        // all callers of addTab that pass a params object need to pass
-@@ -2933,10 +3001,17 @@
+@@ -2933,10 +3002,17 @@
          );
        }
  
@@ -250,7 +258,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        // If we're opening a foreground tab, set the owner by default.
        ownerTab ??= inBackground ? null : this.selectedTab;
  
-@@ -2944,6 +3019,7 @@
+@@ -2944,6 +3020,7 @@
        if (this.selectedTab.owner) {
          this.selectedTab.owner = null;
        }
@@ -258,7 +266,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
  
        // Find the tab that opened this one, if any. This is used for
        // determining positioning, and inherited attributes such as the
-@@ -2996,6 +3072,19 @@
+@@ -2996,6 +3073,19 @@
            noInitialLabel,
            skipBackgroundNotify,
          });
@@ -278,7 +286,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          if (insertTab) {
            // Insert the tab into the tab container in the correct position.
            this.#insertTabAtIndex(t, {
-@@ -3004,6 +3093,7 @@
+@@ -3004,6 +3094,7 @@
              ownerTab,
              openerTab,
              pinned,
@@ -286,7 +294,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
              bulkOrderedOpen,
              tabGroup: tabGroup ?? openerTab?.group,
            });
-@@ -3022,6 +3112,7 @@
+@@ -3022,6 +3113,7 @@
            openWindowInfo,
            skipLoad,
            triggeringRemoteType,
@@ -294,7 +302,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          }));
  
          if (focusUrlBar) {
-@@ -3146,6 +3237,12 @@
+@@ -3146,6 +3238,12 @@
          }
        }
  
@@ -307,7 +315,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        // Additionally send pinned tab events
        if (pinned) {
          this.#notifyPinnedStatus(t);
-@@ -3330,10 +3427,10 @@
+@@ -3330,10 +3428,10 @@
          isAdoptingGroup = false,
          isUserTriggered = false,
          telemetryUserCreateSource = "unknown",
@@ -319,7 +327,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        }
  
        if (!color) {
-@@ -3354,9 +3451,14 @@
+@@ -3354,9 +3452,14 @@
          label,
          isAdoptingGroup
        );
@@ -336,7 +344,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        );
        group.addTabs(tabs);
  
-@@ -3477,7 +3579,7 @@
+@@ -3477,7 +3580,7 @@
        }
  
        this.#handleTabMove(tab, () =>
@@ -345,7 +353,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        );
      }
  
-@@ -3679,6 +3781,7 @@
+@@ -3679,6 +3782,7 @@
          openWindowInfo,
          skipLoad,
          triggeringRemoteType,
@@ -353,7 +361,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        }
      ) {
        // If we don't have a preferred remote type (or it is `NOT_REMOTE`), and
-@@ -3748,6 +3851,7 @@
+@@ -3748,6 +3852,7 @@
            openWindowInfo,
            name,
            skipLoad,
@@ -361,7 +369,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          });
        }
  
-@@ -3935,7 +4039,7 @@
+@@ -3935,7 +4040,7 @@
          // Add a new tab if needed.
          if (!tab) {
            let createLazyBrowser =
@@ -370,7 +378,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
  
            let url = "about:blank";
            if (tabData.entries?.length) {
-@@ -3972,8 +4076,10 @@
+@@ -3972,8 +4077,10 @@
              insertTab: false,
              skipLoad: true,
              preferredRemoteType,
@@ -382,7 +390,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
            if (select) {
              tabToSelect = tab;
            }
-@@ -3985,7 +4091,8 @@
+@@ -3985,7 +4092,8 @@
            this.pinTab(tab);
            // Then ensure all the tab open/pinning information is sent.
            this._fireTabOpen(tab, {});
@@ -392,7 +400,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
            let { groupId } = tabData;
            const tabGroup = tabGroupWorkingData.get(groupId);
            // if a tab refers to a tab group we don't know, skip any group
-@@ -3999,7 +4106,10 @@
+@@ -3999,7 +4107,10 @@
                  tabGroup.stateData.id,
                  tabGroup.stateData.color,
                  tabGroup.stateData.collapsed,
@@ -404,7 +412,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
                );
                tabsFragment.appendChild(tabGroup.node);
              }
-@@ -4044,9 +4154,23 @@
+@@ -4044,9 +4155,23 @@
        // to remove the old selected tab.
        if (tabToSelect) {
          let leftoverTab = this.selectedTab;
@@ -428,7 +436,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
  
        if (tabs.length > 1 || !tabs[0].selected) {
          this._updateTabsAfterInsert();
-@@ -4237,11 +4361,14 @@
+@@ -4237,11 +4362,14 @@
        if (ownerTab) {
          tab.owner = ownerTab;
        }
@@ -444,7 +452,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          if (
            !bulkOrderedOpen &&
            ((openerTab &&
-@@ -4253,7 +4380,7 @@
+@@ -4253,7 +4381,7 @@
            let lastRelatedTab =
              openerTab && this._lastRelatedTabMap.get(openerTab);
            let previousTab = lastRelatedTab || openerTab || this.selectedTab;
@@ -453,7 +461,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
              tabGroup = previousTab.group;
            }
            if (
-@@ -4264,7 +4391,7 @@
+@@ -4264,7 +4392,7 @@
            ) {
              elementIndex = Infinity;
            } else if (previousTab.visible) {
@@ -462,7 +470,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
            } else if (previousTab == FirefoxViewHandler.tab) {
              elementIndex = 0;
            }
-@@ -4292,14 +4419,14 @@
+@@ -4292,14 +4420,14 @@
        }
        // Ensure index is within bounds.
        if (tab.pinned) {
@@ -481,7 +489,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
  
        if (pinned && !itemAfter?.pinned) {
          itemAfter = null;
-@@ -4310,7 +4437,7 @@
+@@ -4310,7 +4438,7 @@
  
        this.tabContainer._invalidateCachedTabs();
  
@@ -490,7 +498,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          if (this.isTab(itemAfter) && itemAfter.group == tabGroup) {
            // Place at the front of, or between tabs in, the same tab group
            this.tabContainer.insertBefore(tab, itemAfter);
-@@ -4338,7 +4465,11 @@
+@@ -4338,7 +4466,11 @@
          const tabContainer = pinned
            ? this.tabContainer.pinnedTabsContainer
            : this.tabContainer;
@@ -502,7 +510,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        }
  
        this._updateTabsAfterInsert();
-@@ -4346,6 +4477,7 @@
+@@ -4346,6 +4478,7 @@
        if (pinned) {
          this._updateTabBarForPinnedTabs();
        }
@@ -510,7 +518,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
  
        TabBarVisibility.update();
      }
-@@ -4635,6 +4767,9 @@
+@@ -4635,6 +4768,9 @@
          return;
        }
  
@@ -520,7 +528,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        this.removeTabs(selectedTabs, { isUserTriggered, telemetrySource });
      }
  
-@@ -4896,6 +5031,7 @@
+@@ -4896,6 +5032,7 @@
          telemetrySource,
        } = {}
      ) {
@@ -528,7 +536,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        // When 'closeWindowWithLastTab' pref is enabled, closing all tabs
        // can be considered equivalent to closing the window.
        if (
-@@ -4985,6 +5121,7 @@
+@@ -4985,6 +5122,7 @@
          if (lastToClose) {
            this.removeTab(lastToClose, aParams);
          }
@@ -536,7 +544,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        } catch (e) {
          console.error(e);
        }
-@@ -5023,6 +5160,12 @@
+@@ -5023,6 +5161,12 @@
          aTab._closeTimeNoAnimTimerId = Glean.browserTabclose.timeNoAnim.start();
        }
  
@@ -549,7 +557,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        // Handle requests for synchronously removing an already
        // asynchronously closing tab.
        if (!animate && aTab.closing) {
-@@ -5037,6 +5180,9 @@
+@@ -5037,6 +5181,9 @@
        // state).
        let tabWidth = window.windowUtils.getBoundsWithoutFlushing(aTab).width;
        let isLastTab = this.#isLastTabInWindow(aTab);
@@ -559,7 +567,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        if (
          !this._beginRemoveTab(aTab, {
            closeWindowFastpath: true,
-@@ -5085,7 +5231,13 @@
+@@ -5085,7 +5232,13 @@
          // We're not animating, so we can cancel the animation stopwatch.
          Glean.browserTabclose.timeAnim.cancel(aTab._closeTimeAnimTimerId);
          aTab._closeTimeAnimTimerId = null;
@@ -574,7 +582,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          return;
        }
  
-@@ -5219,7 +5371,7 @@
+@@ -5219,7 +5372,7 @@
            closeWindowWithLastTab != null
              ? closeWindowWithLastTab
              : !window.toolbar.visible ||
@@ -583,7 +591,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
  
          if (closeWindow) {
            // We've already called beforeunload on all the relevant tabs if we get here,
-@@ -5243,6 +5395,7 @@
+@@ -5243,6 +5396,7 @@
  
          newTab = true;
        }
@@ -591,7 +599,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        aTab._endRemoveArgs = [closeWindow, newTab];
  
        // swapBrowsersAndCloseOther will take care of closing the window without animation.
-@@ -5283,13 +5436,7 @@
+@@ -5283,13 +5437,7 @@
        aTab._mouseleave();
  
        if (newTab) {
@@ -606,7 +614,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        } else {
          TabBarVisibility.update();
        }
-@@ -5422,6 +5569,7 @@
+@@ -5422,6 +5570,7 @@
          this.tabs[i]._tPos = i;
        }
  
@@ -614,7 +622,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        if (!this._windowIsClosing) {
          // update tab close buttons state
          this.tabContainer._updateCloseButtons();
-@@ -5643,6 +5791,7 @@
+@@ -5643,6 +5792,7 @@
        }
  
        let excludeTabs = new Set(aExcludeTabs);
@@ -622,7 +630,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
  
        // If this tab has a successor, it should be selectable, since
        // hiding or closing a tab removes that tab as a successor.
-@@ -5655,13 +5804,13 @@
+@@ -5655,13 +5805,13 @@
          !excludeTabs.has(aTab.owner) &&
          Services.prefs.getBoolPref("browser.tabs.selectOwnerOnClose")
        ) {
@@ -638,7 +646,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        );
  
        let tab = this.tabContainer.findNextTab(aTab, {
-@@ -5677,7 +5826,7 @@
+@@ -5677,7 +5827,7 @@
        }
  
        if (tab) {
@@ -647,7 +655,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        }
  
        // If no qualifying visible tab was found, see if there is a tab in
-@@ -5698,7 +5847,7 @@
+@@ -5698,7 +5848,7 @@
          });
        }
  
@@ -656,7 +664,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
      }
  
      _blurTab(aTab) {
-@@ -6104,10 +6253,10 @@
+@@ -6104,10 +6254,10 @@
        SessionStore.deleteCustomTabValue(aTab, "hiddenBy");
      }
  
@@ -669,7 +677,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          aTab.selected ||
          aTab.closing ||
          // Tabs that are sharing the screen, microphone or camera cannot be hidden.
-@@ -6166,6 +6315,7 @@
+@@ -6166,6 +6316,7 @@
       * @param {MozTabbrowserTab|MozTabbrowserTabGroup|MozTabbrowserTabGroup.labelElement} aTab
       */
      replaceTabWithWindow(aTab, aOptions) {
@@ -677,7 +685,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        if (this.tabs.length == 1) {
          return null;
        }
-@@ -6299,7 +6449,7 @@
+@@ -6299,7 +6450,7 @@
       *   `true` if element is a `<tab-group>`
       */
      isTabGroup(element) {
@@ -686,7 +694,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
      }
  
      /**
-@@ -6375,8 +6525,8 @@
+@@ -6375,8 +6526,8 @@
        }
  
        // Don't allow mixing pinned and unpinned tabs.
@@ -697,7 +705,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        } else {
          tabIndex = Math.max(tabIndex, this.pinnedTabCount);
        }
-@@ -6402,10 +6552,16 @@
+@@ -6402,10 +6553,16 @@
        this.#handleTabMove(
          element,
          () => {
@@ -716,7 +724,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
            if (neighbor && this.isTab(element) && tabIndex > element._tPos) {
              neighbor.after(element);
            } else {
-@@ -6463,23 +6619,28 @@
+@@ -6463,23 +6620,28 @@
      #moveTabNextTo(element, targetElement, moveBefore = false, metricsContext) {
        if (this.isTabGroupLabel(targetElement)) {
          targetElement = targetElement.group;
@@ -751,7 +759,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        } else if (!element.pinned && targetElement && targetElement.pinned) {
          // If the caller asks to move an unpinned element next to a pinned
          // tab, move the unpinned element to be the first unpinned element
-@@ -6492,14 +6653,34 @@
+@@ -6492,14 +6654,34 @@
          //    move the tab group right before the first unpinned tab.
          // 4. Moving a tab group and the first unpinned tab is grouped:
          //    move the tab group right before the first unpinned tab's tab group.
@@ -787,7 +795,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          element.pinned
            ? this.tabContainer.pinnedTabsContainer
            : this.tabContainer;
-@@ -6508,7 +6689,7 @@
+@@ -6508,7 +6690,7 @@
          element,
          () => {
            if (moveBefore) {
@@ -796,7 +804,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
            } else if (targetElement) {
              targetElement.after(element);
            } else {
-@@ -6580,10 +6761,10 @@
+@@ -6580,10 +6762,10 @@
       * @param {TabMetricsContext} [metricsContext]
       */
      moveTabToGroup(aTab, aGroup, metricsContext) {
@@ -809,7 +817,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          return;
        }
        if (aTab.group && aTab.group.id === aGroup.id) {
-@@ -6613,6 +6794,7 @@
+@@ -6613,6 +6795,7 @@
  
        let state = {
          tabIndex: tab._tPos,
@@ -817,7 +825,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        };
        if (tab.visible) {
          state.elementIndex = tab.elementIndex;
-@@ -6639,7 +6821,7 @@
+@@ -6639,7 +6822,7 @@
        let changedTabGroup =
          previousTabState.tabGroupId != currentTabState.tabGroupId;
  
@@ -826,7 +834,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
          tab.dispatchEvent(
            new CustomEvent("TabMove", {
              bubbles: true,
-@@ -6676,6 +6858,10 @@
+@@ -6676,6 +6859,10 @@
  
        moveActionCallback();
  
@@ -837,7 +845,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
        // Clear tabs cache after moving nodes because the order of tabs may have
        // changed.
        this.tabContainer._invalidateCachedTabs();
-@@ -7576,7 +7762,7 @@
+@@ -7576,7 +7763,7 @@
              // preventDefault(). It will still raise the window if appropriate.
              break;
            }
@@ -846,7 +854,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
            window.focus();
            aEvent.preventDefault();
            break;
-@@ -7593,7 +7779,6 @@
+@@ -7593,7 +7780,6 @@
          }
          case "TabGroupCollapse":
            aEvent.target.tabs.forEach(tab => {
@@ -854,7 +862,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
            });
            break;
          case "TabGroupCreateByUser":
-@@ -8542,6 +8727,7 @@
+@@ -8542,6 +8728,7 @@
              aWebProgress.isTopLevel
            ) {
              this.mTab.setAttribute("busy", "true");
@@ -862,7 +870,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
              gBrowser._tabAttrModified(this.mTab, ["busy"]);
              this.mTab._notselectedsinceload = !this.mTab.selected;
            }
-@@ -9543,7 +9729,7 @@ var TabContextMenu = {
+@@ -9543,7 +9730,7 @@ var TabContextMenu = {
      );
      contextUnpinSelectedTabs.hidden =
        !this.contextTab.pinned || !this.multiselected;
@@ -871,7 +879,7 @@ index c0eafd4faf8d57b8486c5bf8917375850ec8147e..1bf95403333f914f082b38441d31326c
      // Build Ask Chat items
      TabContextMenu.GenAI.buildTabMenu(
        document.getElementById("context_askChat"),
-@@ -9863,6 +10049,7 @@ var TabContextMenu = {
+@@ -9863,6 +10050,7 @@ var TabContextMenu = {
          )
        );
      } else {

src/zen/common/ZenUIManager.mjs

@@ -493,20 +493,26 @@ var gZenUIManager = {
 
     if (gURLBar.focused) {
       setTimeout(() => {
-        window.dispatchEvent(
-          new CustomEvent('ZenURLBarClosed', { detail: { onSwitch, onElementPicked } })
-        );
-        gURLBar.view.close({ elementPicked: onElementPicked });
-        gURLBar.updateTextOverflow();
+        setTimeout(() => {
+          window.dispatchEvent(
+            new CustomEvent('ZenURLBarClosed', { detail: { onSwitch, onElementPicked } })
+          );
+          gURLBar.view.close({ elementPicked: onElementPicked });
+          gURLBar.updateTextOverflow();
 
-        // Ensure tab and browser are valid before updating state
-        const selectedTab = gBrowser.selectedTab;
-        if (selectedTab && selectedTab.linkedBrowser && !selectedTab.closing && onSwitch) {
-          const browserState = gURLBar.getBrowserState(selectedTab.linkedBrowser);
-          if (browserState) {
-            browserState.urlbarFocused = false;
+          if (onElementPicked && onSwitch) {
+            gURLBar.setURI(null, onSwitch);
           }
-        }
+
+          // Ensure tab and browser are valid before updating state
+          const selectedTab = gBrowser.selectedTab;
+          if (selectedTab && selectedTab.linkedBrowser && !selectedTab.closing && onSwitch) {
+            const browserState = gURLBar.getBrowserState(selectedTab.linkedBrowser);
+            if (browserState) {
+              browserState.urlbarFocused = false;
+            }
+          }
+        }, 0);
       }, 0);
     }
   },

src/zen/split-view/ZenViewSplitter.mjs

@@ -1067,86 +1067,88 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
    * @param {string|undefined} gridType - The type of grid layout.
    */
   splitTabs(tabs, gridType, initialIndex = 0) {
-    // TODO: Add support for splitting essential tabs
-    tabs = tabs.filter((t) => !t.hidden && !t.hasAttribute('zen-empty-tab'));
-    if (tabs.length < 2 || tabs.length > this.MAX_TABS) {
-      return;
-    }
+    this.#withoutSplitViewTransition(() => {
+      // TODO: Add support for splitting essential tabs
+      tabs = tabs.filter((t) => !t.hidden && !t.hasAttribute('zen-empty-tab'));
+      if (tabs.length < 2 || tabs.length > this.MAX_TABS) {
+        return;
+      }
 
-    const existingSplitTab = tabs.find((tab) => tab.splitView);
-    if (existingSplitTab) {
-      this._moveTabsToContainer(tabs, tabs[initialIndex]);
-      const groupIndex = this._data.findIndex((group) => group.tabs.includes(existingSplitTab));
-      const group = this._data[groupIndex];
-      const gridTypeChange = gridType && group.gridType !== gridType;
-      const newTabsAdded = tabs.find((t) => !group.tabs.includes(t));
-      if (gridTypeChange || !newTabsAdded) {
-        // reset layout
-        group.gridType = gridType;
-        group.layoutTree = this.calculateLayoutTree(
-          [...new Set(group.tabs.concat(tabs))],
-          gridType
-        );
-      } else {
-        // Add any tabs that are not already in the group
+      const existingSplitTab = tabs.find((tab) => tab.splitView);
+      if (existingSplitTab) {
+        this._moveTabsToContainer(tabs, tabs[initialIndex]);
+        const groupIndex = this._data.findIndex((group) => group.tabs.includes(existingSplitTab));
+        const group = this._data[groupIndex];
+        const gridTypeChange = gridType && group.gridType !== gridType;
+        const newTabsAdded = tabs.find((t) => !group.tabs.includes(t));
+        if (gridTypeChange || !newTabsAdded) {
+          // reset layout
+          group.gridType = gridType;
+          group.layoutTree = this.calculateLayoutTree(
+            [...new Set(group.tabs.concat(tabs))],
+            gridType
+          );
+        } else {
+          // Add any tabs that are not already in the group
+          for (let i = 0; i < tabs.length; i++) {
+            const tab = tabs[i];
+            if (!group.tabs.includes(tab)) {
+              gBrowser.moveTabToGroup(tab, this._getSplitViewGroup(tabs));
+              group.tabs.push(tab);
+              this.addTabToSplit(tab, group.layoutTree);
+            }
+          }
+        }
+        if (this._sessionRestoring) {
+          return;
+        }
+        this.activateSplitView(group, true);
+        return;
+      }
+
+      // We are here if none of the tabs have been previously split
+      // If there's ANY pinned tab on the list, we clone the pinned tab
+      // state to all the tabs
+      const allArePinned = tabs.every((tab) => tab.pinned);
+      const thereIsOnePinned = tabs.some((tab) => tab.pinned);
+      const thereIsOneEssential = tabs.some((tab) => tab.hasAttribute('zen-essential'));
+
+      if (thereIsOneEssential || (thereIsOnePinned && !allArePinned)) {
         for (let i = 0; i < tabs.length; i++) {
           const tab = tabs[i];
-          if (!group.tabs.includes(tab)) {
-            gBrowser.moveTabToGroup(tab, this._getSplitViewGroup(tabs));
-            group.tabs.push(tab);
-            this.addTabToSplit(tab, group.layoutTree);
+          if (tab.pinned) {
+            tabs[i] = gBrowser.duplicateTab(tab, true);
           }
         }
       }
+
+      gridType ??= 'grid';
+
+      const splitData = {
+        tabs,
+        gridType,
+        layoutTree: this.calculateLayoutTree(tabs, gridType),
+      };
+      this._data.push(splitData);
+      if (!this._sessionRestoring) {
+        window.gBrowser.selectedTab = tabs[initialIndex] ?? tabs[0];
+      }
+
+      // Add tabs to the split view group
+      let splitGroup = this._getSplitViewGroup(tabs);
+      if (splitGroup) {
+        for (const tab of tabs) {
+          if (!tab.group || tab.group !== splitGroup) {
+            gBrowser.moveTabToGroup(tab, splitGroup);
+          }
+        }
+      }
+
       if (this._sessionRestoring) {
         return;
       }
-      this.activateSplitView(group, true);
-      return;
-    }
-
-    // We are here if none of the tabs have been previously split
-    // If there's ANY pinned tab on the list, we clone the pinned tab
-    // state to all the tabs
-    const allArePinned = tabs.every((tab) => tab.pinned);
-    const thereIsOnePinned = tabs.some((tab) => tab.pinned);
-    const thereIsOneEssential = tabs.some((tab) => tab.hasAttribute('zen-essential'));
-
-    if (thereIsOneEssential || (thereIsOnePinned && !allArePinned)) {
-      for (let i = 0; i < tabs.length; i++) {
-        const tab = tabs[i];
-        if (tab.pinned) {
-          tabs[i] = gBrowser.duplicateTab(tab, true);
-        }
-      }
-    }
-
-    gridType ??= 'grid';
-
-    const splitData = {
-      tabs,
-      gridType,
-      layoutTree: this.calculateLayoutTree(tabs, gridType),
-    };
-    this._data.push(splitData);
-    if (!this._sessionRestoring) {
-      window.gBrowser.selectedTab = tabs[initialIndex] ?? tabs[0];
-    }
-
-    // Add tabs to the split view group
-    let splitGroup = this._getSplitViewGroup(tabs);
-    if (splitGroup) {
-      for (const tab of tabs) {
-        if (!tab.group || tab.group !== splitGroup) {
-          gBrowser.moveTabToGroup(tab, splitGroup);
-        }
-      }
-    }
-
-    if (this._sessionRestoring) {
-      return;
-    }
-    this.activateSplitView(splitData);
+      this.activateSplitView(splitData);
+    });
   }
 
   addTabToSplit(tab, splitNode, prepend = true) {
@@ -1929,6 +1931,17 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
     return true;
   }
 
+  #withoutSplitViewTransition(callback) {
+    this.tabBrowserPanel.classList.add('zen-split-view-no-transition');
+    try {
+      callback();
+    } finally {
+      requestAnimationFrame(() => {
+        this.tabBrowserPanel.classList.remove('zen-split-view-no-transition');
+      }, 0);
+    }
+  }
+
   createEmptySplit() {
     const selectedTab = gBrowser.selectedTab;
     const emptyTab = gZenWorkspaces._emptyTab;
@@ -1975,6 +1988,13 @@ class nsZenViewSplitter extends nsZenDOMOperatedFeature {
       gZenUIManager.handleNewTab(false, false, 'tab', true);
     }, 0);
   }
+
+  get splitViewBrowsers() {
+    if (this.currentView < 0) {
+      return [];
+    }
+    return this._data[this.currentView].tabs.map((tab) => tab.linkedBrowser);
+  }
 }
 
 window.gZenViewSplitter = new nsZenViewSplitter();

src/zen/split-view/zen-decks.css

@@ -58,7 +58,7 @@
   margin-top: 0 !important;
 }
 
-#tabbrowser-tabpanels[zen-split-view='true']:not([zen-split-resizing]) > [zen-split='true'] {
+#tabbrowser-tabpanels[zen-split-view='true']:not(.zen-split-view-no-transition):not([zen-split-resizing]) > [zen-split='true'] {
   transition: inset 0.09s ease-out !important;
   & browser {
     transition: opacity 0.2s ease-out !important;