How does firefox save username/passwords

Well, I have a website with login feature (username and password fields). In firefox, Everytime I start typing username in the username textbox, it throws out suggestions. I then changed the ID and NAME attributes of the textbox. (I made sure the client Id has changed). But the browser still shows the same suggestions. How come? Doesn't the browser relate usernames stored in history to the ID of textbox? I'm using asp.net!

You're thinking of autocomplete, which does work off the field's name.

Firefox login manager looks for forms with password fields. Having found one with between one and three password fields (it may be a "change password" type form, and it wants to prefill those too) it will look for a previous username field. The ids of the fields are irrelevant.