Bug 1055761 - Navigating to a URL can incorrectly switch to an existing browser window

This should solve:

* https://bugzilla.mozilla.org/show_bug.cgi?id=1055761
* https://bugzilla.mozilla.org/show_bug.cgi?id=1055723
* https://bugzilla.mozilla.org/show_bug.cgi?id=1045894