test: Fixed restore tests and fixed possible memory leak on theme modifiers, b=no-bug, c=common, workspaces, tests

src/zen/common/styles/zen-browser-container.css

@@ -8,7 +8,7 @@
   #tabbrowser-tabpanels[dragging-split='true'] {
     width: -moz-available;
     position: relative;
-    overflow: hidden;
+    overflow: clip;
 
     &.browserSidebarContainer {
       :root:not([zen-no-padding='true']) & {

src/zen/common/zenThemeModifier.js

@@ -46,11 +46,15 @@ var ZenThemeModifier = {
       Services.prefs.addObserver(pref, handleEvent);
     }
 
-    window.addEventListener('unload', () => {
-      for (let pref of kZenThemePrefsList) {
-        Services.prefs.removeObserver(pref, handleEvent);
-      }
-    });
+    window.addEventListener(
+      'unload',
+      () => {
+        for (let pref of kZenThemePrefsList) {
+          Services.prefs.removeObserver(pref, handleEvent);
+        }
+      },
+      { once: true }
+    );
   },
 
   handleEvent(event) {

src/zen/tests/workspaces/browser_issue_8699.js

@@ -4,7 +4,10 @@
 'use strict';
 
 add_task(async function test_Restore_Closed_Tabs() {
-  const currentTab = gBrowser.selectedTab;
+  const currentTab = BrowserTestUtils.addTab(window.gBrowser, 'https://example.com/current', {
+    skipAnimation: true,
+  });
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
   const tabsToClose = [];
   for (let i = 0; i < 3; i++) {
     const tab = await BrowserTestUtils.openNewForegroundTab(
@@ -35,7 +38,7 @@ add_task(async function test_Restore_Closed_Tabs() {
     ok(!currentTab.selected, 'Current tab should not be selected after restore');
     Assert.equal(
       gBrowser.tabs.length,
-      5, // 1 initial tab + 3 restored tabs
+      5, // 1 initial tab + 3 restored tabs + 1 for empty tab
       'There should be four tabs after restoring closed tabs'
     );
     gBrowser.selectedTab = currentTab;

src/zen/workspaces/ZenWorkspaces.mjs

@@ -151,14 +151,20 @@ var gZenWorkspaces = new (class extends ZenMultiWindowFeature {
     }
 
     if (!this.privateWindowOrDisabled) {
+      const observerFunction = async function observe(subject) {
+        this._workspaceBookmarksCache = null;
+        await this.workspaceBookmarks();
+        this._invalidateBookmarkContainers();
+      };
       Services.obs.addObserver(this, 'weave:engine:sync:finish');
-      Services.obs.addObserver(
-        async function observe(subject) {
-          this._workspaceBookmarksCache = null;
-          await this.workspaceBookmarks();
-          this._invalidateBookmarkContainers();
-        }.bind(this),
-        'workspace-bookmarks-updated'
+      Services.obs.addObserver(observerFunction, 'workspace-bookmarks-updated');
+      window.addEventListener(
+        'unload',
+        () => {
+          Services.obs.removeObserver(this, 'weave:engine:sync:finish');
+          Services.obs.removeObserver(observerFunction, 'workspace-bookmarks-updated');
+        },
+        { once: true }
       );
     }
   }
@@ -962,7 +968,14 @@ var gZenWorkspaces = new (class extends ZenMultiWindowFeature {
       ) {
         this.log(`Found tab to select: ${this._tabToSelect}, ${tabs.length}`);
         setTimeout(() => {
-          gBrowser.selectedTab = gZenGlanceManager.getTabOrGlanceParent(tabs[this._tabToSelect]);
+          let tabToUse = gZenGlanceManager.getTabOrGlanceParent(tabs[this._tabToSelect]);
+          if (tabToUse.pinned) {
+            // We are before the empty tab here, so we need to select the next tab
+            tabToUse = gZenGlanceManager.getTabOrGlanceParent(
+              tabs[this._tabToSelect + 1] || tabs[this._tabToSelect]
+            );
+          }
+          gBrowser.selectedTab = tabToUse;
           this._removedByStartupPage = true;
           gBrowser.removeTab(this._tabToRemoveForEmpty, {
             skipSessionStore: true,