The only thing you can do is to change all of your passwords. There is nothing anyone can do to help with this.

Does anyone else have access to your system? Are you using sync?

You may have ad/mal-ware. Further information can be found in this article; https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

Did you have logins saved in Firefox that you were sync'ing with your Firefox Account?

If needed, you can try to force an erasure of the contents of the account by resetting your password. See: I've lost my Firefox Sync account information - What to do.

Email is critical, of course. Each provider will have its own instructions for recovering a hacked account, and hopefully you can find those. Good luck!!!