Hello! I've been having similar issues, except not just with firefox. Opera, IE, Firefox, Chrome... None of them can access certain sites. Currently the problem is limited to facebook.com and kingdomofloathing.com
There real kicker is this, though: If I even run a search engine with the words "facebook" or "kingdom of loathing" in it, I get the EXACT SAME error message,
Connection Interrupted
The connection to the server was reset while the page was loading
The network link was interrupted while negotiating a connection. Please try again.
I get a message similar to this on my other browsers. They all say the the page is temporarily unavailable. I have XP professional, SP2, and am running Norton 360 version 2. I don't think this is a firewall issue, though. I've shut my firewall off and turned off any other "protections" provided by my antivirus and still get the same errors.
This problem is limited to my laptop. None of the other computers in my house have this issue.