This is the <font> tag generate by MailNews, when composing mails in html format: <font face="Helvetica, foo, sans-serif"> Usually 'foo' isn't a valid font name... May be it's just a debug let by a lazy programmer? :) So, I suggest, for the next versions, a way to 'save' the font used to edit mails in html format.
should be an editor problem...
Worksforme in build 2002072203 (1.1b) on MacOS 9 : it uses <font face="Helvetica, Arial, sans-serif">
I'm not sure what version of mozilla was used for this original report. This bug was fixed in June. *** This bug has been marked as a duplicate of 150915 ***