Hello, Please see the article [[How to fix preferences that won't save]]. You may have a ''user.js'' file setting that preference each time you start up Firefox. Information on how to remove it is in the article above, or more specifically this section: * https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save#w_user-js-file-overriding-preferences If you have no ''user'js'' file, the article shows other possible reasons why the preference keeps getting reset.