Comment 29 for bug 490935

In addition to being able to edit the subject line for the incoming mail
summary (not in the msg header), some users need to be able to insert a short
note into the body of the msg for future reference. For example, I receive
many technical newsletters and E-mails, and often insert short notes (like a
footnote) referring to some URL or other E-mail for related information.
The lack of this feature in Mozilla Thunderbird is a major reason preventing
me from switching. Eudora has this toggle - the Pencil button toggle, which
makes it possible to save it to the original msg.
Thunderbird has an "Edit this message as new" feature, but it saves the
modified msg separately in a different format, but it's clunky & doubles the
storage space required..