The mail.strictly_mine fix does not make ????'s go away permanently. I agree with observation of Walt.
The mail.strictly_mime fix to make question marks appearing in emails went away for a few days. However, the ????s started appearing again. I checked the mail.strictly_mime parameter and it is still set at "true". I'm on TB 60.8.0. This is the latest version for Windows 7.
Additional System Details
- Shockwave Flash 32.0 r0
- User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0
You inadvertently posted this on the Firefox support forum - I will ask a moderator to move this to Thunderbird support.