This issue is not solved for me, running thunderbird's latest version on
Sid's repository.
I run an XFCE DE with no Display Manager. I login in a tty, and then
startx. Maybe it has something to do with that.
As for the other binaries suggested to run here, I have no different
results. And line "deny @{HOME}/.* r" is not present in
/usr/bin/thunderbird.
Terminal output when running thunderbird is:
No protocol specified
Unable to init server: Could not connect: Connection refused
Error: cannot open display: :0.0
