How To Downgrade Firefox Add-ons

 It sometimes happens that one of your favorite add-ons gets an update that you are not happy about. A new add-on version can for instance break functionality, introduce changes that you do not want or decrease the browser’s stability or security. If you do not want to uninstall the affected add-on, you could consider installing an older version of it to overcome the issue that you are experiencing... "

Source: Ghacks Technology Newsletter
 How To Downgrade Firefox Add-ons