I have an HP a1330n running XP. Lately, I'm finding it very slow accessing Firefox. I am up to date on the latest version. Firefox itself seems to be slower loading than before but once to a website you pull your hair out waiting for it to change pages. I'm getting a "connecting" message in the upper left corner with the spinning icon. After 3 or 4 minutes it may change pages and sometimes if I hit the "X" on the address bar and then hit the reload current page (in the same location as the X I just mentioned) it will change.
I have McAfee and it's up to date also - it tells me I'm protected. I've run Spybot also and it tells me I'm clean.
What else can I tell you or what other info do you need?