only prints subject line, cannot print message body
For some unknown reason, only the subject line prints. No header nor message text.
I uninstalled Firefox and reinstalled from the website. No change.
Earlier today, I was able to print whole email messages.
I then went to another computer (and printer) and opened my email account and was able to print the whole message correctly.
Alla svar (1)
I assume that you are trying to print e-mails from Thunderbird, not Firefox as you say.
Try Print Preview (Menu: File: Print Preview), and see if it also shows the same thing.
Oh, by the way, have you tried rebooting the computer yet to see if the problem exists after the reboot?