Restore browser-polyfill.js

src/browser-polyfill.js

@@ -6,11 +6,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 "use strict";
 
-if (typeof window != "object" || typeof chrome != "object" || !chrome || !chrome.runtime || !chrome.runtime.id) {
-  throw new Error("This script should only be loaded in a browser extension.");
-}
-
-if (typeof window.browser === "undefined" || Object.getPrototypeOf(window.browser) !== Object.prototype) {
+if (typeof browser === "undefined" || Object.getPrototypeOf(browser) !== Object.prototype) {
   const CHROME_SEND_MESSAGE_CALLBACK_NO_RESPONSE_MESSAGE = "The message port closed before a response was received.";
   const SEND_RESPONSE_DEPRECATION_WARNING = "Returning a Promise is the preferred way to send a reply from an onMessage/onMessageExternal listener, as the sendResponse will be removed from the specs (See https://developer.mozilla.org/docs/Mozilla/Add-ons/WebExtensions/API/runtime/onMessage)";
 
@@ -544,6 +540,10 @@ if (typeof window.browser === "undefined" || Object.getPrototypeOf(window.browse
     return wrapObject(extensionAPIs, staticWrappers, apiMetadata);
   };
 
+  if (typeof chrome != "object" || !chrome || !chrome.runtime || !chrome.runtime.id) {
+    throw new Error("This script should only be loaded in a browser extension.");
+  }
+
   // The build process adds a UMD wrapper around this file, which makes the
   // `module` variable available.
   module.exports = wrapAPIs(chrome);