Preds,
Check your Firefox version. I'm currently on the most recent release 1.0.6. Try a fresh install of the the latest version (remove your current version, go to getfirefox.com and download the most recent version).
In Tools > Options, try these settings:
General > Connection Settings: Direct Connection to the Internet
Privacy: Clear All
Web Features: everything checked except Load Images for the originating web site only
Advanced > Software Update - check all the "periodically check" options and then Check Now button.
Advanced > Security - check SSL 2.0, SSL 3.0, TLS 1.0
Also check out this mozillaZine:
http://kb.mozillazine.org/Error_loading_any_website