After user signup, Firefox offers to save the password but not for the correct username

In my user signup form, I have a text field named twitter_username. After the form is submitted (for example, with the_real_shaq in the twitter username field), Firefox did this:

Do you want Firefox to remember the password for "the_real_shaq" on heroku.com?

Obviously I Firefox to offer to store the password for user's username on m开发者_如何学运维y site, not their supplied twitter username. How can I do this? Thanks for reading.

As far as I know this depends on the browser. A good thread is at this thread. User "bta" has a good paragraph on how Firefox finds the username text box. This may require a re-arrangement of your user interface though. Hope this helps!