changing font style on internet browsers

hey there...

i just want to know how do i change the font style on the internet browsers i am using on mac.i have been using both safari and firefox and both of them have this irritating looking font, that's very hard to read especially on google and yahoo search results page. I have tried to change the fonts on both browsers already using their preferences menu but nothing seems to work. The font styles don't change. please help.. i think even if i use another browser aside from the two that i've mentioned, it would still be the same. maybe the problem is not on the browser but on the mac itself. so how do i fix that? please help. thanks.

here's how it looks anyway..

http://boxstr.com/files/4290353_lktji/Picture%201.png

do you have arial font installed on your mac ... ?