Looks like on firefox 3.5 they have made something really wrong, two mates at work are also complaining about it, memory hunger and cpu takeover, I haven't upgraded yet, due to some plugins not ready for 3.5, looks like is a lucky me.
Some people know about my opera preference, well, it was until some upgrade somewhere early this year, freaked it up and all I got was a an opera eating 500mb ram with 5 or so sites open and I need about 30.
Lets see if they manage to find the problm and fix it soon.