With some graphics cards a compositor (compositing manager) is needed to fix
tearing.
I am using XFCE DE, but the default compositing manager doesn't help, so I
use compton.
It is a standalone program, so you may be able to use it with most window
managers, thereby most DE-s.
Unfortunately it is not in the Trisquel repo, so you need to use a PPA:
https://launchpad.net/~richardgv/+archive/compton
or get the source:
https://github.com/chjj/compton
Note that you may need to configure it, and it may require experimentation
for best result.
