Bug 1539979 - Initialize browser-loader only after domready in toolbox.js;r=bgrins

Depends on D26319

Differential Revision: https://phabricator.services.mozilla.com/D26320

--HG--
extra : moz-landing-system : lando

devtools/client/framework/toolbox.js

@@ -449,11 +449,6 @@ Toolbox.prototype = {
    */
   open: function() {
     return (async function() {
-      this.browserRequire = BrowserLoader({
-        window: this.doc.defaultView,
-        useOnlyShared: true,
-      }).require;
-
       const isToolboxURL = this.win.location.href.startsWith(this._URL);
       if (isToolboxURL) {
         // Update the URL so that onceDOMReady watch for the right url.
@@ -493,6 +488,11 @@ Toolbox.prototype = {
       this._threadClient = await attachThread(this);
       await domReady;
 
+      this.browserRequire = BrowserLoader({
+        window: this.win,
+        useOnlyShared: true,
+      }).require;
+
       // The web console is immediately loaded when replaying, so that the
       // timeline will always be populated with generated messages.
       if (this.target.isReplayEnabled()) {