how can I sign in, if I don't have an account to sign in with?
Well, just trying to ask this question solved the problem... sort of. I needed to know how to create this account. You have NO easy way to figure that out. The only way I could figure it out was to ask how to do it as a problem that I could not solve. I suggest that you put a "CREATE NEW ACCOUNT" button somewhere easily seen so others don't have this same problem.
Todas as respostas (2)
You are among many with the same complaint. Welcome Aboard.
You can click the "Volunteer for Mozilla Support" button on the https://support.mozilla.org page to go to the https://support.mozilla.org/get-involved page.