Bug 1832748 - Make click consistently hit space between urlbar and nav bar. r=dao

It seems that 1px offset isn't consistently for our synthesized click to
hit where it's supposed to. There's a 4px gap between urlbar and navbar
so let's increase this a bit.

Differential Revision: https://phabricator.services.mozilla.com/D206881

browser/components/customizableui/test/browser_customization_context_menus.js

@@ -172,7 +172,7 @@ add_task(async function urlbar_context() {
   let shownPromise = popupShown(contextMenu);
   let urlBarContainer = document.getElementById("urlbar-container");
   // Need to make sure not to click within an edit field.
-  EventUtils.synthesizeMouse(urlBarContainer, 100, 1, {
+  EventUtils.synthesizeMouse(urlBarContainer, 100, 2, {
     type: "contextmenu",
     button: 2,
   });