I find as does everyone I have converted to it find firefox to be both faster and more efficient than anything else. Have you for a second considered the age of your computer maybe being a reason or spy/malware being involved?
I use Kerio from Sunbelt. You get a 30-day trial of the full version, then you buy, or it drops down to the free version - which is fine for home use. I tried Comodo just recently, but had problems (which may be because of external factors which just co-incided with the problems).