> Also, I just found out that you can use
>
> pref("mailnews.send_plaintext_flowed", false);
>
> to make Mozilla send your plain text messages without "format=flowed" in
> the header.
>
> Anyone else think this should be the default?
>
No, not if it's the display you have trouble with. Format=flowed is a
widely used standard out there, even though it's not seen much in news
since the main producers (Hotmail and Eudora) are mail only. That means
that you will still see the format regardless of which format you use
yourself when sending.
The workaround you probably want is to is to treat incoming
format=flowed mails as format=fixed mails. There is another pref for
that (see in all.js or mailnews.js or wherever the default prefs are
stored).
The real fix though is to file and fix the bugs making your experience
with incoming f=f mails a less than perfect one. I know there are some,
mainly concerned with the impossibility to control the width of the text
without changing window size. (Myself have the opposite problem with
non f=f mails wrapping the last word on every line because Mozilla
displays the text with a too big font)
/Daniel