Hi

Typically, if you email has been hacked, it is your on-line email account rather than your browser, however I would recommend changing any passwords for any other on-line accounts that use the same password and/or email address and also to have a read of this article to make sure your copy of Firefox (and your computer generally) is secure.

I hope this helps, but if not, please come back here and we can look into a different solution for you.

Well said.

Make sure you are using a good anti-virus program. Many of them have the option to scan your e-mails.