Oh, the reason is in your log:
Feb 27 16:40:07 kg-Studio-1737 thunderbird[7543]: Error: cannot open
display: :0
That means U8/Libertine failed to launch Xmir (or wait for Xmir) prior
to running thunderbird.
** Changed in: libertine (Ubuntu)
Importance: Undecided => High
** Changed in: unity8
Incomplete for Xmir. Running it manually from ssh launches successfully:
mirrun Xmir :1 -rootless --desktop_file_hint=unity8 & sleep 2 ; env
DISPLAY=:1 thunderbird
So it sounds like U8 or Libertine isn't launching it correctly.
** Changed in: gtk+3.0 (Ubuntu)
Status: Confirmed => Invalid
