crash id's? https://support.mozilla.org/en-US/kb/mozilla-crash-reporter-tb#w_viewing-crash-reports

Mac users like to use the word crash, but this user is describing a hang. I didn't find an open bug report which describes this, but I don't doubt that these steps could cause a hang. Similar to https://bugzilla.mozilla.org/show_bug.cgi?id=635565

Yes, it is definitely a hang and not a crash.

I had originally let it work for a minute or two and it did not resolve itself. However, the last time it happened I let it go for about 4 minutes and eventually it became usable again. The attachment did not get attached to the email I was writing and if I tried again, it would hang again.

Again, saving the attachment from my inbox email to the desktop allowed it to be dragged from the desktop to the email I was writing without any issues.

It is certainly not an issue on windows, I can not reproduce at all. But I would assume that Thunderbird would be writing a temp file somewhere probably at the location specified in the TMP or TEMP environment variables. Could something be interfering with that I wonder. Any software, like an anti virus that would be monitoring temp files

I suspect this is a Mac dialog issue, so it is not surprising it doesn't occur on Windows (which I confirm)