If you have sync, and there is a problem anywhere, Shut Down Sync Immediately to prevent the problem from spreading. Once the problem is fixed, perform the same repair on all computers before using sync again.

You may have ad / mal-ware. Further information can be found in the Troubleshoot Firefox issues caused by malware article.

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

Go to any website you think was accessed and use the Forgot Password link to create new passwords.

Hopefully the malware cleaning software will help (see link in Fred's reply).

If not, do you have a local Seniors/community center? Often someone teaches computer classes there who might be able to provide local assistance or suggest someone locally who does. I mention that because there probably are dozens of questions that we would have to exchange doing this through written Q&A format when you have problem with lots of different accounts.