Comment 86 for bug 195698

(In reply to comment #36)
> This seems to be an issue caused by extensions. While we could try to
> bulletproof things, I suspect that multiple MP prompts are caused by repeated
> attempts to access the software token in NSS. We can't fix that on the front
> end, since this seems like an extension bug.
>

This isn't a problem caused by extensions at least not since Firefox 2.0.x. It can be recreated with no extensions installed (in a brand new profile). The simplest way to do so is to have Firefox remember password and set it up to "restore windows and tabs from last time".

At this point, open two windows: one with 1 tab open and one with 2 tabs open. Make sure Firefox has a saved password for Google and then open the following URL in all 3 tabs:

https://www.google.com/accounts/LoginAuth?continue=http%3A%2F%2Fwww.google.com%2F&hl=en

Finally use he File->Exit command. The next time you open Firefox it will show multiple password prompts.

An interesting note, it won't show multiple prompts if there are simply 2 windows open (1 tab each) or if there is one window open with 2 tabs. I'm not sure why.