I cannot duplicate that. I highlight and copy from incoming message, then open a new write window and select edit>paste and the content is entered as anticipated.

Thank you.

I tried pasting into a new write window, and that worked.

In fact, the problem seems to have gone away now.

I will continue to monitor it to see if it has gone away permanently or is somehow intermittent.

I continue to have this problem from time to time.

It occurred yesterday, but it went away (I think that I quit/restarted TB).

It has happened again today, and quit/restart has not helped.

Viewing message source and copying from there does not work either.

Can anyone recommend anything diagnostic that I can do when the problem occurs to try to figure out what might have happened?

For diagnostic purposed try the following. That will eliminate Thunderbird's addons, as well as some other Thunderbird "features" and the operating systems non safe mode processes in turn

• Does Thunderbird work as expected in Thunderbird troubleshooting mode?
• Does Thunderbird work as expected with your OS started in safe mode with Networking. Instructions for each operating system: Windows 10/11, Windows 8, Windows 7, OSX