[BlibbityBlabbity]

I think that pops up with a little window the first time you enter a password asking "do you want firefox to remember this password" (or close to that) and then the next time you come to that site, assuming you logged off the time before, it would either be blank and then when you started typing your user name the list of close matches comes up and when you choose one the password comes in automatically.

If you said no to that pop up the first time and checked the do not ask me again box it will never come up again. I think you can reset that by clearing one of the caches in options, but that would reset ALL your site information at all sites, so if you do have them saved at many other sites you would have to reenter all of them again.

there might be a way to erase the setting one site at a time, but i have never tried it.