Just found that when using PasswordMaker that it is causing the autocomplete to have 2 blank entries in some cases in Firefox. I'm not sure if they are actually blank entries or if the autocomplete part is just expanding or what. The following was done on a brand new profile, only PasswordMaker installed:
Then if you uninstall PasswordMaker, it goes back to normal:
If you want to reproduce, just go to paypal.com, then type in asdf/asdf for email/password, then when you get to the next screen, double click in the email textbox. It happens on other sites too.