I have Windows XP, and use Earthlink cable for my internet.
First, make sure that your version of Firefox is up to date. Recent Windows fixes might have broken your installation. Your big problem, however, might be the cable connection. If a few kids in the neighborhood are playing online games, they may be chewing up the available bandwidth on your part of the network. Everything will appear slow if that’s the case.
I had similar problems. My wifes PC would not get out but our Macs could get out albeit somewhat sporadically and slow.
Change your DNS settings to OpenDNS (free at basic level)
Open DNS is 22.214.171.124 and 126.96.36.199
Once I did that problem resolved. Earthlink customer service really sucks and I dread having to talk to them
I had good luck with PC Pitstop Optimize 3.0 from the PC Pitstop website. Please stay away from Finally Fast from the AD on TV, it is useless and should be sued out of existance.
Also, the CCleaner free download can be found on MajorGeeks.com. I use version 2.27.1070 currently, but it’s updating often. Run it just before you shut down every day.