How You can do this?
Autofill Forms plugin for FireFox.
Just download it:
Configure all necessary rules form and submitaddons.mozilla.org/pl/firefox/addon/autofill-forms/
This one is for e-mail forms
really great thing when You dont have budget for commercial software.( mail|(?:^email$)|(?:^emailconfirm$)|(?:^email$)|ma il_url|(?:^data\[Post\]\[email\]$)