Fixing this requires minimal refactoring in a test which can be executed easily. It would make a great first bug for a new contributor.

Currently browser/base/content/test/popupNotifications/browser_popupNotification_3.js calls addTabsProgressListener()[1] to wait for onLocationChange[2] to occur. This listens for onLocationChange in all tabs, where the test really only cares about a single <browser>[3].

To listen for just the single browser we care about we should be calling addProgressListener()[4] instead. This involves replacing where addTabsProgressListener is called[5] with addProgressListener. Also the call to removeTabsProgressListener[6] will need to be replaced with removeProgressListener.

As mentioned in bug 915951 comment 58, it looks like the onLocationChange handler[7] might depend on something running in another onLocationChange handler. In order to ensure the test's handler runs second, we should also call 'executeSoon()'[8] to run our code.

Lastly, since we now know we are only listening to onLocationChange for the correct browser, we can get rid of the code that checks the browser in the onLocationChange handler[9]

This test can be executed from the firefox source repository by running:
 ./mach mochitest-browser browser/base/content/test/popupNotifications/browser_popupNotification_3.js


[1] https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/Method/AddTabsProgressListener
[2] https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/Reference/Interface/nsIWebProgressListener#onLocationChange%28%29
[3] https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/browser


[4] https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/Method/addProgressListener
[5] http://mxr.mozilla.org/mozilla-central/source/browser/base/content/test/popupNotifications/browser_popupNotification_3.js?rev=1f51eb900e57#264
[6] http://mxr.mozilla.org/mozilla-central/source/browser/base/content/test/popupNotifications/browser_popupNotification_3.js?rev=1f51eb900e57#259

[7] http://mxr.mozilla.org/mozilla-central/source/browser/base/content/test/popupNotifications/browser_popupNotification_3.js?rev=1f51eb900e57#249
[8] executeSoon is a helper function which "Executes a function shortly after the call, but lets the caller continue working (or finish)."

[9] http://mxr.mozilla.org/mozilla-central/source/browser/base/content/test/popupNotifications/browser_popupNotification_3.js?rev=1f51eb900e57#250