I saw a msg asking about how to not accidentally close Thunderbird when
closing last tab. The msg is gone from the Mozi server now it seems, but
in case the poster still needs this info-
One can un-check "close window on delete", and carefully,
Go to tools/options/advanced/config editor. The item copied below is
#1262 (at least on my system), of more than 1800 settings.
(change to "false"
Save setting by entering on OK.
Never change more than one setting at a time in config editor unless you
are _very sure of what you're doing.
This should work for you.