When I tried to enter my firefox account, my e-mail adress was deleted, because I didn't log in in it for a long time, so the confirmation mail went nowhere.

Try following the instructions here: https://support.mozilla.org/en-US/kb/im-having-problems-confirming-my-firefox-account Specifically, since you've now recovered the email, you should be able to resend the confirmation and use it, right? '''Click the Resend email link on the Firefox Sync signup page. '''