More as a reminder to myself, but possibly also helpful to other people who want to use Firefox on a tablet running Debian...
Without the below adjustment, finger gestures in Firefox running on a tablet result in image moving, text highlighting, etc. (operations related to copy+paste). Not the intuitively expected behaviour...
If you use e.g. GNOME on Wayland for your tablet and want to enable touch functionalities in Firefox, then switch the whole browser to native Wayland rendering. This line in ~/.profile seems to help:
export MOZ_ENABLE_WAYLAND=1
If you use a desktop environment running on top of X.Org, then make sure you have added the following line to ~/.profile:
export MOZ_USE_XINPUT2=1
Logout/login again and Firefox should be scrollable with 2-finger movements up and down, zooming in and out also works then.
light+love
Mike (aka sunweaver at debian.org)