Issue 5315 - Add support for Microsoft Edge

ext/popup.js

 "use strict";
 
 (function()
 {
-  if (!chrome || !chrome.extension)
+  if (typeof chrome == "undefined" || typeof chrome.extension == "undefined")
     window.chrome = browser;
   const backgroundPage = chrome.extension.getBackgroundPage();
   window.ext = Object.create(backgroundPage.ext);
 
   window.ext.closePopup = () =>
   {
     window.close();
   };
+
+  // Calling i18n.getMessage from the background page causes Edge to throw an
+  // exception.
+  // https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12793975/
+  window.ext.i18n = chrome.i18n;
 
   // We have to override ext.backgroundPage, because in order
   // to send messages the local "chrome" namespace must be used.
   window.ext.backgroundPage = {
     sendMessage: chrome.runtime.sendMessage,
 
     getWindow()
     {
       return backgroundPage;
     }
   };
 }());