Sorry for the multiple replies but I just found another oddity if you're using KDE.
In system-setttings, if you have personalization-->Regional Settings-->Formats
"Detailed Settings" checked and alter Time it will override whatever you have
in your .bashrc.
You can see this, or check, by finding the PID of your T-Bird process, go to /proc/PID and
cat environ and check what LC_TIME is set to.
--
Sorta what I want to say when folks habitually complain about Fedora -
https://youtu.be/ZArl8fTfub4