I think Nightly isn't a Official part of the FF forum here that is a separate from FF itself and you need to contact the Nightly Forum about this problem.

WestEnd said

I think Nightly isn't a Official part of the FF forum here that is a separate from FF itself and you need to contact the Nightly Forum about this problem.

Nightly just refers to one of the development channels of Firefox. Release < Beta (b#) < Nightly (a1). There is also the Developers edition (Aurora) that is same as Beta but with additional dev features. There is no Nightly forum.

https://www.mozilla.org/firefox/channel/desktop/

Savant.Superman said

Firefox Nightly keeps asking for my Master Password! I think it's hacked! No matter if I upgrade it, it keeps happening. Please help!

The more bleeding edge Nightly channel builds of Firefox gets checkins with two updates each day. This can lead to issue(s) until fixed, finished, or reverted.

You could create and account and post in http://forums.mozillazine.org/viewforum.php?f=23 where Testers hang out as not a many Testers hang out here at Sumo. Note if you do not have an account there new members first post requires post approval due to spamming.