Check with your ISP in their security section. My ISP (Comcast) offers the new full-blown Norton Security Suite for FREE! It used to be McAfee but they switched to Norton when the new non-bloat resource hog version came out last year. I also use Firefox only as a web browser and have had zero issues in the last five years. I used to run both AVG free and Zone Alarm but they were far from perfect.
I've used PC Tools' "Spyware Doctor w/Antivirus" for several years with no problems....
The one computer in my house that had McAfee on it (only because it came with it and was free for a year) kept getting trojans on it, but all that stopped with Spyware Doctor and Firefox....
I have to keep Internet Explorer on this machine because one of the business programs I use won't work with Firefox....