Try a new profile first.
On Linux or Mac, start Firefox with the the -profilemanager switch, e.g. ./firefox -profilemanager (this assumes that you're in the firefox directory).
Firefox screwed up on me a few months ago where it would not go to certain webpages, and creating a new profile fixed the problem.
Just curious, but what version of Firefox are you using? The latest at least for the Beta is 1.0.6-9. Installing a newer version if you can might help.
Standard diagnostic - MozillaZine Knowledge Base
You should also check /etc/resolv.conf to make sure it has the correct DNS nameservers listed.
They should be the same ones your router uses. You can add different ones as well.
If none of the above work, completely uninstall; making sure to delete all of the directories.
These are the important files you might want to save:
# bookmarks.html Bookmarks.
# prefs.js Current user preferences.
# user.js User-added preferences (overrides prefs.js every startup).
# cookies.txt Cookies.
# hostperm.1 Cookies permissions, image permissions, and extension website install permissions list.
# signons.txt Saved passwords. Requires the "key3.db" file to work.
# key3.db Supplements password file.
Then reinstall using YAST/YOU.