Hello everybody, jkwong888 at https://github.com/Bumblebee-Project/Bumblebee/issues/580 came up with a fix that actually solves the problem - at least for me.
Turns out that appending the following screen-section to /etc/bumblebee/xorg.conf.nvidia makes bumblebee work: Section "Screen" Identifier "Default Screen" Device "DiscreteNvidia" EndSection After a restart of bumblebeed, optirun works properly. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org