Comment 5 for bug 890177

Following further tests, to replicate start a Reply to the message, position cursor at start of message and hit enter. Each hit of enter causes a 40 second processor lockup.
@Alan, if that does not do it could you try it in plain text mode? I think from your screenshot you are in html. I can't work out how to set Thunderbird to html format to try that myself. It is probably hidden somewhere in plain sight.