On Mac the scroll bars can be hidden and only have them show when you scroll the page so you can see the current scroll position. The idea is that a touch pad is used that doesn't require the scroll bars to be visible and thus have more screen estate for the browsing area. You can make the scroll bars always visible: System Preferences > General > Show Scroll Bar > Choose "Always" You can try to delete the xulstore.json file in the Firefox profile folder. You can use this button to go to the currently used Firefox profile folder: *Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder) *http://kb.mozillazine.org/Profile_folder_-_Firefox