AVG and MalWareBytes here.
No issues on my old WXP SP# box.
Running Ghostery as well on FF v.40.0.3 along with AdBlocker.
BTW, “BitDefender” is the best rated AV program and they offer a 30-day free trial.
I would probably switch, but I have a paid version courtesy of my job of AVG that’s good thru next year.