This is related to the question I asked here: http://stackoverflow.com/questions/2382329/how-can-i-get-browser-to-prompt-to-save-password

This is the problem: I CAN'T get my browser to prompt me to save the password for the site I'm developing. (I'm talking about the bar that appears sometimes when you submit a form on Firefox, that says "Remember the password for yoursite.com? Yes / Not now / Never")

This is super frustrating because this feature of Firefox (and most other modern browsers, which I hope work in a similar fashion) seems to be a mystery. It's like a magic trick the browser does, where it looks at your code, or what you submit, or something, and if it "looks" like a login form with a username (or email address) field and a password field, it offers to save.

Except in this case, where it's not offering my users that option after they use my login form, and it's making me nuts. :-)

(I checked my Firefox settings-- I have NOT told the browser "never" for this site. It should be prompting.)

My question: exactly what the heuristics are that Firefox (or any other modern browser) uses to know when it should prompt the user to save? This shouldn't be too difficult to answer, since it's right there in the Mozilla source (I don't know where to look or else I'd try to dig it out myself). You'd think there would be a blog post or some other similar developer note from the Mozilla developers about this but I can't find that either.

(* Note that if your answer to me has anything to do with cookies, encryption or anything else that is about how I'm storing the user's passwords in the database, you've probably misread my question. :-)