Firefox 4 should be a lot faster than Firefox 3.6.x. If that isn't happening then you may have extensions that aren't working properly or other profile problems. Some security software that doesn't recognize the Firefox 4 version as trusted can also cause a slow response. So check that as well. ---- Create a new profile as a test to check if your current profile is causing the problems.<br /> See: * [[Basic Troubleshooting#Make_a_new_profile|Basic Troubleshooting&#58; Make a new profile]] There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" If that new profile works then you can transfer some files from the old profile to that new profile (be careful not to copy corrupted files) See http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox