I have used this email address since I started using email

Hi rmervine, I can't figure out the context of your question. Are you having trouble registering on a Mozilla site? or maybe the fact that I see this post means the problem has been solved by now. Please let us know if you still need help.

Won't let me use my email address.

Hi rmervine, do you mean you can't create a Firefox account with your email address? Does it give you a specific error message that might help us figure out what's going on?

No, I was filling out a form. They asked what my email address was but then the form told me that what I wrote was not my email address.

I was filling out your form. It asked what my email address was and when I typed it in I was told that what I typed was not my email address.

Hi

Are you trying to access your Firefox Account and are you selecting the option to use an existing account or to set up a new account?