After upgrading to Thunderbird 115.6.0 (from some prior version) on Linux Mint 20.1 LTS, we noticed the body of the email text was defaulting to a small size. You could Increase Font Size, and that would increase the font size for both the header and window, but also the email body. But when you closed the email and reopened it, the header and window font size stayed what you set it to, but the email body text displayed in the same small size. Interestingly, when you then say "Decrease Font Size", it would make the text larger, in line with the header and window font size shrinking by one notch. Zoom likewise increases the font size of the email body, but it doesn't persist. I've tried the recommendations for going into custom settings and changed to default the properties that were recommended, but that did not seem to fix the issue. Any help or suggestions would be appreciated. Michael