I encountered this behavior on a private site so I can't link to an example, but if you know one please let me know and I will add it here.
Is there a way to prevent this from happening, and force every window created by JS to have the full interface of a normal Firefox window? Is there a way to get controls back? I believe Chrome for instance has a menu command for it, but I'm not sure about FF.
NB: I am actually on Waterfox but let's answer for Firefox and hopefully it will apply to the forks as well.