Recently, the scrollbar behavior of my Firefox web browser changed.   The “old” (and expected/desired) behavior is that if you click in the scrollbar area anywhere below the thumb, the thumb moves down one page.

However, the new behavior is that a normal click will “Warp” the thumb directly to the clicked location, scrolling the webpage a whole lot farther than desired.   (it used to be that a right-click would do the “warp”, which is a useful feature, not not necessarily one I want to be the default).

I found the answer here: https://support.mozilla.org/en-US/questions/1120904

The change in behavior is caused by gtk 3.0 and to fix it on Ubuntu Linux, I had to:

create ~/.config/gtk-3.0/settings.ini

with contents:

[Settings]

gtk-primary-button-warps-slider = false