Fóram Tacaíochta Firefox

So on my macbook when I enable fullscreen the anmation is super weird. first it stretches the video to the top and then just expands to the whole screen, when I go out of fullscreen is stretches to the bottom and then goes out off fullscreen. for example on safari it just expands the video until it takes up the whole screen. I have gone in about:config and disabled the fullscreen animation but that did nothing.

When logging into an account there are multiple usernames (incorrect or older.) I would like to remove or delete them, but keep the current passwords.

Is that possible without deleting the account?

Thank you, rldelahay

New install of Firefox set up with a 'wrong' email account. Tried to use the 'Mozilla account' page to fix this by using secondary email and then making it primary. But the secondary email I want to use is not allowed by Firefox giving an 'Account already exists' error. What should I do?