diff --git a/README.md b/README.md
index fe060d312..cd81cbc0e 100644
--- a/README.md
+++ b/README.md
@@ -30,7 +30,7 @@
 
 Zen is currently built using Firefox version `138.0.4`! 🚀
 
-- [`Zen Twilight`](https://zen-browser.app/download?twilight) - Is currently built using Firefox version `RC 138.0.4`!
+- [`Zen Twilight`](https://zen-browser.app/download?twilight) - Is currently built using Firefox version `RC 139.0`!
 - Check out the latest [release notes](https://zen-browser.app/release-notes)!
 - Part of our mission is to keep Zen up-to-date with the latest version of Firefox, so you can enjoy the latest features and security updates!
 
diff --git a/build/firefox-cache/l10n-last-commit-hash b/build/firefox-cache/l10n-last-commit-hash
index 5ec4a514c..714d02686 100644
--- a/build/firefox-cache/l10n-last-commit-hash
+++ b/build/firefox-cache/l10n-last-commit-hash
@@ -1 +1 @@
-f5fd58c29d2c9bfcc5dcfc8f4abbe69016e13b44
\ No newline at end of file
+82a08ea3ce2d17f21f3d45f4b5607a37590b0158
\ No newline at end of file
diff --git a/src/browser/base/moz-build.patch b/src/browser/base/moz-build.patch
index ce28f4aaf..257879b43 100644
--- a/src/browser/base/moz-build.patch
+++ b/src/browser/base/moz-build.patch
@@ -1,9 +1,9 @@
 diff --git a/browser/base/moz.build b/browser/base/moz.build
-index 636e0841786735a63ddea00e819c0b6f0b8a5d4d..62e4531bd19caf098fd76c69b213fa32d62546a6 100644
+index 9da444880c4dbf188443d43e8d0a71d98311a2b7..3a654be6f78931e92479b30de6f0a6e50da81908 100644
 --- a/browser/base/moz.build
 +++ b/browser/base/moz.build
-@@ -87,3 +87,5 @@ if CONFIG["MOZ_WIDGET_TOOLKIT"] in ("windows", "gtk"):
-     DEFINES["MENUBAR_CAN_AUTOHIDE"] = 1
+@@ -81,3 +81,5 @@ DEFINES["MOZ_APP_VERSION_DISPLAY"] = CONFIG["MOZ_APP_VERSION_DISPLAY"]
+ DEFINES["APP_LICENSE_BLOCK"] = "%s/content/overrides/app-license.html" % SRCDIR
  
  JAR_MANIFESTS += ["jar.mn"]
 +
diff --git a/src/browser/components/tabbrowser/content/tabbrowser-js.patch b/src/browser/components/tabbrowser/content/tabbrowser-js.patch
index dfaaacb14..31324eeec 100644
--- a/src/browser/components/tabbrowser/content/tabbrowser-js.patch
+++ b/src/browser/components/tabbrowser/content/tabbrowser-js.patch
@@ -222,8 +222,8 @@ index 6dece2b9d0462d90a28e75350ce983d87816ef73..5c49c43714b3914130f8d821d902f9f2
 +          t.setAttribute("zen-empty-tab", "true");
 +        }
          if (insertTab) {
-           if (typeof index == "number") {
-             elementIndex = this.#tabIndexToElementIndex(index);
+           // Insert the tab into the tab container in the correct position.
+           // For now, we support `index` as an alias for `tabIndex`.
 @@ -2779,6 +2846,7 @@
            openWindowInfo,
            skipLoad,
@@ -245,25 +245,8 @@ index 6dece2b9d0462d90a28e75350ce983d87816ef73..5c49c43714b3914130f8d821d902f9f2
        // Additionally send pinned tab events
        if (pinned) {
          this._notifyPinnedStatus(t);
-@@ -2945,12 +3019,15 @@
-      * @param {string} [label=]
-      * @returns {MozTabbrowserTabGroup}
-      */
--    _createTabGroup(id, color, collapsed, label = "") {
-+    _createTabGroup(id, color, collapsed, label = "", pinned = false, essential = false, splitViewGroup = false) {
-       let group = document.createXULElement("tab-group", { is: "tab-group" });
-       group.id = id;
-       group.collapsed = collapsed;
-       group.color = color;
-       group.label = label;
-+      group.pinned = pinned;
-+      group.essential = essential;
-+      if (splitViewGroup) group.setAttribute('split-view-group', true);
-       return group;
-     }
- 
 @@ -2993,10 +3070,10 @@
-         insertBefore = null,
+         isAdoptingGroup = false,
          isUserTriggered = false,
          telemetryUserCreateSource = "unknown",
 +        forSplitView = false,
@@ -275,9 +258,9 @@ index 6dece2b9d0462d90a28e75350ce983d87816ef73..5c49c43714b3914130f8d821d902f9f2
  
        if (!color) {
 @@ -3011,7 +3088,12 @@
-         id = `${Date.now()}-${Math.round(Math.random() * 100)}`;
-       }
-       let group = this._createTabGroup(id, color, false, label);
+         label,
+         isAdoptingGroup
+       );
 -      this.tabContainer.insertBefore(
 +      if (forSplitView) {
 +        group.setAttribute('split-view-group', true);
@@ -386,21 +369,21 @@ index 6dece2b9d0462d90a28e75350ce983d87816ef73..5c49c43714b3914130f8d821d902f9f2
        if (tabs.length > 1 || !tabs[0].selected) {
 @@ -3912,7 +4030,7 @@
        // Ensure we have an index if one was not provided.
-       if (typeof index != "number") {
+       if (typeof elementIndex != "number" && typeof tabIndex != "number") {
          // Move the new tab after another tab if needed, to the end otherwise.
--        index = Infinity;
-+        index = Services.prefs.getBoolPref("zen.view.show-newtab-button-top") ? this._numVisiblePinTabsWithoutCollapsed : Infinity;
+-        elementIndex = Infinity;
++        elementIndex = Services.prefs.getBoolPref("zen.view.show-newtab-button-top") ? this._numVisiblePinTabsWithoutCollapsed : Infinity;
          if (
            !bulkOrderedOpen &&
            ((openerTab &&
 @@ -3935,7 +4053,7 @@
            ) {
-             index = Infinity;
+             elementIndex = Infinity;
            } else if (previousTab.visible) {
--            index = previousTab.elementIndex + 1;
-+            index = (typeof previousTab.elementIndex === 'undefined') ? index : (previousTab.elementIndex + 1);
+-            elementIndex = previousTab.elementIndex + 1;
++            elementIndex = (typeof previousTab.elementIndex === 'undefined') ? index : (previousTab.elementIndex + 1);
            } else if (previousTab == FirefoxViewHandler.tab) {
-             index = 0;
+             elementIndex = 0;
            }
 @@ -3958,18 +4076,18 @@
  
@@ -413,12 +396,12 @@ index 6dece2b9d0462d90a28e75350ce983d87816ef73..5c49c43714b3914130f8d821d902f9f2
        } else {
 -        index = Math.max(index, this.pinnedTabCount);
 +        index = Math.max(index, this._numVisiblePinTabsWithoutCollapsed);
-         index = Math.min(index, this.tabContainer.ariaFocusableItems.length);
+         index = Math.min(index, allItems.length);
        }
  
        /** @type {MozTabbrowserTab|undefined} */
--      let itemAfter = this.tabContainer.ariaFocusableItems.at(index);
-+      let itemAfter = this.tabContainer.ariaFocusableItems.filter(tab => !tab.hasAttribute("zen-glance-tab")).at(index);
+-      let itemAfter = allItems.at(index);
++      let itemAfter = allItems.filter(tab => !tab.hasAttribute("zen-glance-tab")).at(index);
        this.tabContainer._invalidateCachedTabs();
  
 -      if (tabGroup) {
diff --git a/surfer.json b/surfer.json
index 2088c338c..8ae2fc155 100644
--- a/surfer.json
+++ b/surfer.json
@@ -6,7 +6,7 @@
   "version": {
     "product": "firefox",
     "version": "138.0.4",
-    "candidate": "138.0.4"
+    "candidate": "139.0"
   },
   "buildOptions": {
     "generateBranding": true