Thanks for feedback. That's a pity that it cannot be fixed in Enigmail for the latest stable Thunderbird ESR release. In general that's bad news especially for people in companies which need to use an ESR release or cannot always use the latest development/beta releases. Do you know the bug-fix in the upcoming Thunderbird?
I already submitted the crash report to Mozilla. Crash report ID: 059ba0d3-cf40-492e-a4ec-f52c40190311
I attached all the crash details (without email address).
Thunderbird crash when send a signed but not encrypted email with empty message
Thunderbird crash when send a signed but not encrypted email with empty message