Hi my name is ***** ***** to JustAnswer. I am reviewing your question and will reply ASAP.
It's not very clear what the issue is. Is the Font too small or the Font too big? We could begin right away removing Font files from your system and Thunderbird preferences to troubleshoot the problems you have with Thunderbird. This would be not be a good idea without knowing what the issues are.Is there a specific reason to use Thunderbird over Mac Mail?
Have you tested it in a new user account?We could try a remote desktop connection to troubleshoot the issue as it would make visualising the problem a lot easier.Let me know how you would like to proceed. Thanks!
I would recommend Mac Mail over Thunderbird.It sounds like there are a few different issues in Thunderbird so would suggest a new user account to help highlight if it is user specific or system wide. The troubleshooting could be in-depth, or with remote connection it could be easy to identify.If you change your mind please don't hesitate to get back to me.Kind regards,