Thanks, it works now!
However, there's one tiny problem.. and one I can't really report properly.
On the very left of my screen, there's a 1 pixel wide strip that is sometimes pink-ish, sometimes blue-ish. It's definitely not a monitor defect, as when I play LFS with default shaders, it does not appear, nor does it appear anywhere else.
The most stupid thing is that it does not gets captured by screenshots. Therefore I can't even show it properly.
Any idea what it could be?