I need information on how to use Firefox

If your using to post on Firefox forum with firefox Browser you already know how to use it. For site other that require sign you need to be registed or create a account to sign on their site. Firefox can't help one with signing to other sites. You need to contact that site webmaster for help with their site instead.

You can check this article:

• https://support.mozilla.org/en-US/kb/fix-login-issues-on-websites-require-passwords