Try upgrading to the latest version of firefox if possible using "yum upgrade firefox". Do you have any additional Firefox plugins installed? If so you may have to disable some or all of them, and enable them one by one to see which one is causing the issue.
sudo yum install firefox
Loaded plugins: dellsysidplugin2, priorities, refresh-packagekit
Setting up Install Process
Package firefox-3.5.3-1.fc11.x86_64 already installed and latest version
Nothing to do
i am on the latest version. Firefox freezes the screen before it's even fully up so i can't change any firefox settings