If Firefox disabled some add-ons (especially extensions), it likely is because they include a list of compatible Firefox versions and haven't yet been updated for Firefox 5. For more information on avast, see this thread: [https://support.mozilla.com/en-US/questions/841934 I have just updated Firefox on my desktop. In order to operate it had to disable avast, my open source excellent anti virus software - a surprise that Firefox is compatible! Is there an avast! update that is compatible? Or a fix from Firefox coming? | Firefox Support Forum | Firefox Help].