Changing date format in Thunderbird
Create a small bash file
and cut and paste the following in it.
#!/bin/sh export LC_TIME=en_GB exec /usr/bin/thunderbird "$@
Then make the file executable and edit the launcher
chmod 774 ~/thunder gnome-desktop-item-edit /usr/share/applications/mozilla-thunderbird.desktop
and replace the command with ~/thunder i.e. the path of the above file.
Note: unfortunately you will have to repeat the last command after each upgrade