How is user name defined? Is it my e-mail address and is the password that of my e-mail account?

Hi eneg, your accounts can have different styles of user names. Some use your email address, but others let you create a different name (harder for someone trying to break into your account to learn).

What kind of account are you trying to set up or log into? Normally, Firefox doesn't require you to sign in. However, this Support site does need you to create an account, so if that's what you meant, it seems you have already solved the problem.