hello, this might happen when firefox is not able to properly save preferences in its profile folder. please try this: Click the menu button ≡ and then click help ? > troubleshooting information > profile folder - "show folder". then a new window will open up. in this window look out for a file named '''user.js''' (it might be used to overwrite your custom settings). in case it is present , delete or rename this file and restart firefox afterwards. for more information and other steps please also see: [[How to fix preferences that won't save]]