The one thing I HATE about Thunderbird is how hard it is to simply paste something into an email. Apparently once you paste it (say from excel) you can't undo the paste, you can't delete it, and you cannot type anything below what you pasted (which is how I found you can neither undo or delete what you pasted). Invariably, I have to delete the whole email and start over. Surely that is not how it was intended to function.