I recently had quite a bit of trouble with my computer. I reinstalled Windows more than once, and have eventually got everything working again. I used Backupfox to save all my Firefox settings, but when i restored the settings into my new install of Firefox, all my passwords were gone.
Although the box was ticked to save passwords, and there were no websites on the ‘exceptions’ list, and my signons2.txt file was there with all my passwords (in encrypted format), Firefox was not asking me whether i wanted to save a new password, or remembering my old ones.
In the end, i deleted the signons2.txt file and now it seems to be working again! Thankfully i remember most of my passwords!