Ok, I know there has got to be a FireFox extension for this or something.
What I need is something where I can manually add in POST variables to a page that gets submitted when I submit the page. I am doing this to see if I can get by my Anti-Spam mod for phpBB2 that sends a die() message if the user enters in a variable that is hidden(I am hiding everything that is not needed on the registration page). But the problem is I can't fill anything in to test it easily.