> It would be preferable to submit a patch to Debian so that autopkgtest
> understands Devuan releases (as it currently appears to for Ubuntu).
> There are already a few Debian packages that have accepted such patches.

Thanks for your quick clarification.
A major blocker to use autopkgtest on Devuan to test a Devuan package
(e.g. thunderbird or firefox) is #461. I have no idea on how to work around #461,
and without a workaround or a right fix to #461, fixes to #459 or #460
do not have much value, as autopkgtest remains completely unusable with
qemu testbed, besides #459 and #460 have easy workarounds.

I will put my effort on #460 after #461 finds a workaround or a fix.

Best regards, Ryutaroh