This question has already been asked (How to fix GTK3 scrollbar behavior) but I don't know how to implement the answer: If I click in the scrollbar below or above the thumb it moves to the spot I just clicked. This happens in Firefox but not in Opera, the 2 browsers I use. Could someone explain how to fix the problem?
What you want is called "legacy scrolling" in gtk3: edit or create
$HOME/.config/gtk-3.0/settings.ini to have
as the first line and
on a subsequent line by itself. This works in most gtk3 applications but is said not to work in some. Alternatively, right-click instead of left-clicking works in all applications. And, if you want legacy scrolling system-wide, sudo edit
/etc/gtk-3.0/settings.ini the same way.
You can find out where got changed; during GTK v3.6 merge.
Kristian Rietveld and Michael Natterer introduced the feature but both had since dropped out of GitHub. :-/