As of late 2018, there is now limited customization available in Firefox!
See these answers:
- https://stackoverflow.com/a/54101063/405015
- https://stackoverflow.com/a/53739309/405015
And this for background info: https://bugzilla.mozilla.org/show_bug.cgi?id=1460109
There’s no Firefox equivalent to ::-webkit-scrollbar and friends.
You’ll have to stick with JavaScript.
Plenty of people would like this feature, see: https://bugzilla.mozilla.org/show_bug.cgi?id=77790
As far as JavaScript replacements go, you can try:
- https://github.com/mdbootstrap/perfect-scrollbar
- https://github.com/Grsmto/simplebar
- https://github.com/vitch/jScrollPane