Rated 5 out of 5 stars

I love the Print-action. This makes my work easier.

This review is for a previous version of the add-on (2.0). 

Yeah, I just fixed it for Thunderbird 78, see:
https://github.com/RealRaven2000/FiltaQuilla/releases/tag/3.0pre44

I might need to do some back-porting for THunderbird 68 too, not sure if all features still work there.