The firefox diff that broke this for conkeror is here:

https://hg.mozilla.org/mozilla-central/diff/6a563348b8be/toolkit/components/passwordmgr/nsLoginManagerPrompter.js

I believe the problem is that mozilla has replaced the getBrowser method with gBrowser throughout the
firefox code base. But conkeror only defines getBrowser in windows.js (line 200). 

Furthermore, there is a new getBrowserForContentWindow method that we need to define. See this seamonkey
bug for an example:

https://api-dev.bugzilla.mozilla.org/show_bug.cgi?id=1300539