(Ubuntu 10.04 · Thunderbird 17.0.5)
I read all my mails as plain text (View → Message Body As → Plain text). Usually they all are in the same font with the same font size:
But once in a while I get a mail which is displayed in a different font/font size:
At Edit → Preferences → Display → Formatting → Advanced… I have the same settings for all languages/charsets. I also deactivated "Allow messages to use other fonts".
What is the reason for the font difference?
The encoding of this particular mail seems to be Chinese Simplified (GB2312), at least according to View → Character Encoding. So I changed every font setting for Simplified Chinese (to test it), but nothing changed in the mail.
At this thread the solution (for TB 13) was to change the font settings for Other Languages. But I don't have this option in the list.