How does browser know when to prompt user to save password?

Question

This is related to the question I asked here: 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

What are the heuristics that Firefox 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). I've also had no luck finding a blog post or some other similar developer note from the Mozilla developers about this.

(I would be fine with this question being answered for Safari or IE; I would imagine that all the browsers user very similar rules, so if I can get it working in one of them, it will work in the others.)

(* Note that if your answer to me has anything to do with cookies, encryption or anything else that is about how I'm storing passwords in my local database, odds are strong that you have misunderstood my question. :-)

Answer 1

Based off what I have read, I think Firefox detects passwords by form.elements[n].type == "password" (iterating through all form elements) and then detects the username field by searching backwards through form elements for the text field immediately before the password field (more info here). You might try something similar in Javascript and see if you can detect your password field.

From what I can tell, your login form needs to be part of a <form> or Firefox won't detect it. Setting id="password" on your password field probably couldn't hurt either.

If this is still giving you a lot of problems, I would recommend asking on one of the Mozilla project's developer mailing lists (you might even get a response from the developer who designed the feature).