Hi, I'm still on Windows 10, so I can't test this, but could you try it: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button accepting the risk. ''More info on about:config:'' [[Configuration Editor for Firefox]]. ''The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.'' (2) In the search box in the page, type or paste '''scrollbar.''' and pause while the list is filtered ''Firefox should display 10-12 preferences.'' (3) Double-click the '''widget.non-native-theme.win.scrollbar.''use-system-size''''' preference to switch the value from true to false ''With that preference set to false, you should be able to set your own width...'' (4) Double-click the '''widget.non-native-theme.scrollbar.''size.override''''' preference to display an editing field, and change the value to '''17''' then press Enter or click the blue check mark button to save the change. Note: 17 is based on Windows 10. You can use whatever value makes you happy. If you reset it back to 0, it will use the OS default width. Does that work? There's also one other interesting one you could experiment with. This affects the appearance but, as far as I can tell, not the width: (5) Double-click the '''widget.non-native-theme.scrollbar.style''' preference to display an editing field, and change the value to '''4''' then press Enter or click the blue check mark button to save the change. With this preference, "0" follows the system default, "4" should follow Firefox's "Windows 10" theme, and "5" should follow Firefox's "Windows 11" theme.