Any Idea whats wrong with my mac?

The other day I was on the internet via firefox and every time i went to random internet pages, firefox would freeze and not unfreeze, making me have to force quit it. After several more attempts at going back on firefox the same thing would happen every time i went to specific random sites (random because there was no reason for those sites to make firefox crash). Assuming firefox was just being buggy I went on safari, however the same thing would happen when I went to random website (some sites that crashed firefox wouldn't crash safari and vice versa). So after a day or two of irritating web browser crashes I got the mcafee anitvirus program and scanned my mac. The scan ended with it finding one virus file and removing it. However my internet browsers continued crashing the same as before. I then tried uninstalling firefox and downloading it again, hoping that it would work better. It runs just as bad as before and now it takes a minute or two to open.

So basically I have no idea what's going wrong with my mac and I was wondering if you have any ideas as to what the problem is/how to fix it.