--- a/testing/mochitest/browser-test.js
+++ b/testing/mochitest/browser-test.js
@@ -84,20 +84,30 @@ Tester.prototype = {
         else
           this.dumper.dump("TEST-UNEXPECTED-FAIL | (browser-test.js) | " + msg + "\n");
 
         win.close();
       }
     }
 
     // Make sure the window is raised before each test.
-    let self = this;
-    this.SimpleTest.waitForFocus(function() {
-      aCallback.apply(self);
-    });
+    if (this._fm.activeWindow != window) {
+      this.dumper.dump("TEST-INFO | (browser-test.js) | Waiting for window activation...\n");
+      let self = this;
+      window.addEventListener("activate", function () {
+        window.removeEventListener("activate", arguments.callee, false);
+        setTimeout(function () {
+          aCallback.apply(self);
+        }, 0);
+      }, false);
+      window.focus();
+      return;
+    }
+
+    aCallback.apply(this);
   },
 
   finish: function Tester_finish(aSkipSummary) {
     this._cs.unregisterListener(this);
 
     if (this.tests.length) {
       this.dumper.dump("\nBrowser Chrome Test Summary\n");