After more investigation, it turns out that there are two different bugs. One in FF 46 (this exact bug) was about an invisible scroll bar, which got fixed in a later version. The other newer bug started in FF 52, which is currently about a very thin scroll bar that regressed in 52 and later (see the screenshots in bug #1675496).
I have changed the duplicates accordingly. ** Changed in: firefox (Ubuntu) Status: Confirmed => Fix Released -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1575896 Title: Scrollbar thumb not drawn in Firefox 46 and later (gtk3?) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1575896/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs