Firefox nonobviousity: Type in about:config in your address bar Search for widget.non-native-theme.scrollbar.size.override Edit it to whatever number you want You can also edit widget.non-native-theme.scrollbar.style to change the shape of it, set it to 4 for a nice chonk rectangle Finally, turn on “Always show scrollbars” in the normal settings window about:settings if you want them always on.