Version 69.0.2 is the latest Firefox. Are you sending mail through your browser, Firefox, or Thunderbird? There's no need to add the pref. to TB - it's already there.

Thanks for the quick reply. I'm sending emails through Thunderbird...

What is your version of TB? Help/About TB. Who is the mail provider for the outgoing server?

Version 68.1.1 smtp.aol.com (They took over Verizon.net emails)

I have an AOL account, and switching the preference eliminates the ?? in sent mail. Check under Tools/Options/Display/Formatting/Advanced... and set Text Encoding for outgoing mail to Unicode (UTF-8).

https://support.mozilla.org/en-US/questions/1260169#answer-1225235

Settings were already set to UTF-8

Thanks, sfhowes! I tested email this AM and ???? were no longer showing up. No settings were changed so they must've been scared off when they knew someone with your expertise was on the case. Thanks again. I won't be dumping TB after all... Mike