I personally can't deduce the problem you have on such limited information. Maybe resetting your browser will help. I do resetting on a regular basis. I recently cleaned my friends' browser doing this since he had a malicious extension installed, so instead of deleting it, I reset it. Reset gives you a fresh copy of Firefox without losing your bookmarks, history, passwords. If it doesn't help, you should make efforts to scan and clean your computer if infected. If that doesn't work as well, format it.