Have you ever mistyped your login name in firefox, only to have it save the wrong entry as well as the correct one? How do you get rid of the wrong entry? You could clear out all of your saved information, but why just for one mistake! Frustrating huh? Even more frustrating is finding the completely undocumented answer. Well I’m documenting it now.
Go to the form where the mistake is. Put your cursor in the text entry widget and hit down until the incorrect entry is highlighted. Now press shift + del … voila. You’re welcome.