Please update to Firefox 45, and let us know if you still have any questions. [[Update Firefox to the latest version]]

Also, your Question Details > More System Details to the right of your post shows an optional settings file named user.js file in your profile folder (personal settings folder). Firefox uses the settings in that file at startup to override your saved preferences from the previous session. Unless you created that file yourself, it may contains settings from an add-on or external software tha undo changes you make. You can check and remove the file using the steps in this article: [[How to fix preferences that won't save]]. By default, Windows hides the .js file extension. To work with files as accurately as possible, I suggest show all file extensions. This Microsoft support article has the steps: [http://windows.microsoft.com/en-us/windows/show-hide-file-name-extensions].