Judy are you running Ad block plus on Firefox? You may also be able to disable some of your alerts in advanced settings, but it is not recommended. AVG seems to be the most compatible anti-virus I've found for Firefox. I too, ran Avast when I ran Explorer but switched back after some issues. Norton, I've always found to be a PITA.
The only program I have a problem with is my Corel, it keeps jamming up on my XP Pro but runs fine on Holly's Win 8.1.
