built-in middle button is not the same as on a mouse
Before I upgraded my Thinkpad T420 to Debian 9, I was able to use the
middle mount/trackpad button on my laptop to grab and scroll things in
applications like evince (pdf viewer) and Kicad (circuit board designer).
Now the middle button will work for pasting and opening a link in a new
tab, but won't work for grab-and-scroll.
I use MATE as my desktop environment and have gone through all the
configuration stuff to no avail. What am I missing?