The last time I tried Firefox, it didn't render some links properly. It also was not compatible with my very nice, two wheel, 5 button mouse. Most of the extra mouse functions wouldn't work, it was like I was using a plain old cheap $5 mouse. It wouldn't communicate with my printer either. So I went back to IE.
I ran Norton Internet Security for years, updating every couple years when the new version came out. Then it got too bloated and slowed down my computer too much. 
When I got my new computer, I bought AVG Internet Security. About a month ago, AVG insisted that I upgrade to the newest version (popup balloons constantly reminding me to upgrade) but when I upgraded, I wasn't able to access the internet at all. I tried uninstalling and reinstalling 3 times and the problem was their stupid security program. So I deleted it and then downloaded the AVG free version. WOW! Everything got a lot faster and the Windows built in security stuff takes up the slack. Windows even has a built in spam filter for your email that works a lot better than the AVG program I paid for. 
In conclusion, I think the AVG free version is all I need (combined with some common sense when surfing). In 10 years of daily surfing with high dollar security programs, they only caught 3 viruses. Two were in emails and one was a corrupt web page. But the free AVG combined with the built in Windows Vista tools (Windows Defender and the email filter) will deal with any similar threat.