Hello,
the setup is
* debian 10
* default gnome on wayland
* fresh install
the problem occurs with firefox-esr and firefox-esr -safe-mode
when
* using an attached monitor as primary
* using the laptop monitor as secondary with hipdi scale 200%
on the primary monitor the firefox resolution is as expected,
on the de secondary monitory firefox ignores the scaling factor of 200%
(resulting in a really small display)
other info: other applications don't seem to have this problem,
like terminator, nautilus, libreoffice,..
hth,
Wim