Bug 1824140 - Only allow left click on PiP urlbar button. r=pip-reviewers,mhowell

Differential Revision: https://phabricator.services.mozilla.com/D174139

toolkit/components/pictureinpicture/PictureInPicture.sys.mjs

@@ -466,6 +466,10 @@ export var PictureInPicture = {
    * @param {Event} event Event from clicking the PiP urlbar button
    */
   toggleUrlbar(event) {
+    if (event.button !== 0) {
+      return;
+    }
+
     let win = event.target.ownerGlobal;
     let browser = win.gBrowser.selectedBrowser;