Bug 1918681 - part 1: Allow moving the list-all-tabs button again r=dao

In bug 878551, the ability to move the list-all-tabs button was	removed
for a few reasons:

> Moving this widget to the navbar gives it a tiny scaled version of Toolbar.png (like a horizontal line).

> Moving it back to the tab strip make it misbehave. It disappears, but sometimes flickers into view when opening/closing a tab.

These issues are no longer present, so we should be able to allow moving
the list-all-tabs button once again.

Differential Revision: https://phabricator.services.mozilla.com/D224623

browser/base/content/browser-init.js

@@ -154,10 +154,7 @@ var gBrowserInit = {
     // We don't want these normally non-removable elements to get put back into the
     // tabstrip if we're initializing with vertical tabs
     if (isVerticalTabs && !isPopup) {
-      nonRemovables = [
-        gBrowser.tabContainer,
-        document.getElementById("alltabs-button"),
-      ];
+      nonRemovables = [gBrowser.tabContainer];
       for (let elem of nonRemovables) {
         elem.setAttribute("removable", "true");
         // tell CUI to ignore this element when it builds the toolbar areas

browser/base/content/navigator-toolbox.inc.xhtml

@@ -90,7 +90,7 @@
                        delegatesanchor="true"
                        badged="true"
                        data-l10n-id="tabs-toolbar-list-all-tabs"
-                       removable="false"/>
+                       removable="true"/>
       </hbox>
     </hbox>
 

browser/components/customizableui/CustomizableUI.sys.mjs

@@ -4194,7 +4194,6 @@ var CustomizableUIInternal = {
 
     // Normally these aren't removable, but for this operation only we need to move them
     changeWidgetRemovability("tabbrowser-tabs", true);
-    changeWidgetRemovability("alltabs-button", true);
 
     if (toVertical) {
       lazy.log.debug(
@@ -4249,7 +4248,6 @@ var CustomizableUIInternal = {
     );
     this.setToolbarVisibility(CustomizableUI.AREA_TABSTRIP, !toVertical);
     changeWidgetRemovability("tabbrowser-tabs", false);
-    changeWidgetRemovability("alltabs-button", false);
 
     for (let [win] of gBuildWindows) {
       win.TabBarVisibility.update(true);

browser/modules/test/browser/browser_UsageTelemetry_toolbars.js

@@ -203,6 +203,7 @@ add_task(async function widgetPositions() {
       "stop-reload-button",
       "tabbrowser-tabs",
       "personal-bookmarks",
+      "alltabs-button",
     ],
 
     "nav-bar": [
@@ -249,7 +250,7 @@ add_task(async function customizeMode() {
   organizeToolbars({
     PersonalToolbar: ["personal-bookmarks"],
 
-    TabsToolbar: ["tabbrowser-tabs", "new-tab-button"],
+    TabsToolbar: ["tabbrowser-tabs", "new-tab-button", "alltabs-button"],
 
     "nav-bar": [
       "back-button",
@@ -344,7 +345,7 @@ add_task(async function contextMenus() {
   organizeToolbars({
     PersonalToolbar: ["personal-bookmarks"],
 
-    TabsToolbar: ["tabbrowser-tabs", "new-tab-button"],
+    TabsToolbar: ["tabbrowser-tabs", "new-tab-button", "alltabs-button"],
 
     "nav-bar": [
       "back-button",