[openbox] system fonts have become much larger

[Louis-David Mitterrand]

Hi,

On a debian 'testing' system I'm using openbox with gdm3 as session
manager launching via ~/.xsession with 'exec openbox-session'.

Recently after a reboot the system fonts have become much larger:
application title bars and menu fonts (firefox, libreoffice, etc.) as
well as openbox's own menu fonts. Also I've had to reduce my xterm font
from point size 11 to 9 to have terminals of the same size as before
(firefox pages still display the same, no font size increase there).

It's probably not an openbox issue per se but since users here are
pretty knowledgeable, any idea where to look is welcome.

Thanks,