Comment 24 for bug 610915

There are actually two separate problems covered by this bug. You may have found a third, actually... The two I know of are the case where the saved username has the incorrect case stored, and the case where the user wishes to save two different usernames for the same site, that differ only by case. In the first of these, the user can delete the bad entry from the stored passwords list, so it isn't a problem, really. The second case is the one that I would say requires backing out 447788.
Assuming your (Thom) problem is caused by the saved password list, then you just need to go to the Preferences/Options Security tab, under saved passwords.
The possible third case that you may be introducing would be if your problem is being introduced by the form entry memory feature, in which case it is probably a separate bug