feat: Don't search clipboard content when middle clicking the sidebar, b=no-bug, c=no-component

src/browser/base/content/navigator-toolbox-js.patch

@@ -1,5 +1,5 @@
 diff --git a/browser/base/content/navigator-toolbox.js b/browser/base/content/navigator-toolbox.js
-index 15469e9d9b91c1eaef2578c9e43b6999edac3392..553402b41bc15f7cd99bf87c54416dc66d7c03e7 100644
+index 15469e9d9b91c1eaef2578c9e43b6999edac3392..95ae5036b57baeb5237603c0921f1e9252af6919 100644
 --- a/browser/base/content/navigator-toolbox.js
 +++ b/browser/base/content/navigator-toolbox.js
 @@ -6,7 +6,7 @@
@@ -19,15 +19,25 @@ index 15469e9d9b91c1eaef2578c9e43b6999edac3392..553402b41bc15f7cd99bf87c54416dc6
          #picture-in-picture-button,
          #urlbar-zoom-button,
          #star-button-box,
-@@ -206,6 +207,7 @@ document.addEventListener(
-         case "vertical-tabs-newtab-button":
-         case "tabs-newtab-button":
-         case "new-tab-button":
-+        case "zen-tabs-wrapper":
+@@ -209,6 +210,17 @@ document.addEventListener(
            gBrowser.handleNewTabMiddleClick(element, event);
            break;
  
-@@ -318,6 +320,7 @@ document.addEventListener(
++        case "zen-tabs-wrapper":
++          if (event.button == 1) {
++            BrowserCommands.openTab();
++            // Stop the propagation of the click event, to prevent the event from being
++            // handled more than once.
++            // E.g. see https://bugzilla.mozilla.org/show_bug.cgi?id=1657992#c4
++            event.stopPropagation();
++            event.preventDefault();
++          }
++          break;
++
+         case "back-button":
+         case "forward-button":
+         case "reload-button":
+@@ -318,6 +330,7 @@ document.addEventListener(
          #downloads-button,
          #fxa-toolbar-menu-button,
          #unified-extensions-button,
@@ -35,7 +45,7 @@ index 15469e9d9b91c1eaef2578c9e43b6999edac3392..553402b41bc15f7cd99bf87c54416dc6
          #library-button,
          #split-view-button
        `);
-@@ -401,6 +404,16 @@ document.addEventListener(
+@@ -401,6 +414,16 @@ document.addEventListener(
            gUnifiedExtensions.togglePanel(event);
            break;