RedneckDude and I moved away from Avast back when it started deleting/killing his DX widgets (in some cases, with no notice or warning at all.) Up to that point, it had served us well. Once Avast decided it was going to take things over in spite of its users wishes, it was on its way out.
If anyone is looking for a good, less obnoxious Antivirus program, and need it to be free, give AVG 2015 a try. I've switched to it on 2 rigs and have been very happy with its performance so far. It is lightweight and only does what I tell it to do. I can't vouch for the Firefox addon problems since I don't use FF but you may want to at least give it some thought.