Symantec are due to release updates very soon to make their add-ons work in Firefox 4.0.1. For details see http://community.norton.com/t5/Norton-Internet-Security-Norton/Norton-product-compatibility-with-Firefox-Updates/m-p/443808 ----- Pending this update, you can go back to Firefox 4.0, their add-ons work in that version. You can get Firefox 4.0 from http://releases.mozilla.org/pub/mozilla.org/firefox/releases/4.0/win32/ - you need to select the folder for your language, you can then download and run the Firefox 4 setup file to install it. If you do install Firefox 4.0 temporarily turn off automatic updates until Symantec update their add-ons. To do that in the Firefox options window, go to the Advanced panel, and then the Update tab and de-select the option to automatically check for updates to Firefox.