> I sometimes find myself writing a new message (which defaults to plain
> text -I believe I've configured this in the settings, which is what I
> want for the most part) only to find out that I need it to be stylizing
> in HTML instead. A "switch between plain text/HTML" button in the
> toolbar area would be nice.
>
> I'm using Thunderbird 3.1.20 (the latest version possible on my PPC Mac)
> but haven't so far found anything like that compatible with my version.
Hold down shift whilst clicking on Write, Forward or Reply to toggle to
the alternative (non-default) mode.
Of course, this relies on you accurately remembering which is the
default mode for each account. And that you can decide upfront which
mode you need. ;)
There are add-ons that provide a drop-down button so you can make an
explicit choice when replying. Paolo Kaosmos has several at his nicnac site:
https://nic-nac-project.org/~kaosmos/index-en.html#frwas
https://nic-nac-project.org/~kaosmos/realborders-en.html
...and maybe:
https://nic-nac-project.org/~kaosmos/changequote-en.html
I don't know of such a button for your situation when you're writing a
/new/ message. In theory, HTML mode has a menu selection to enable plain
text: *Options|Format|Plain Text Only*
...but ISTR that it doesn't generate pure plain text.
I suspect that plain text and HTML modes are sufficiently different that
it would be non-trivial to switch between them on the fly. I imagine it
would have to compose in rich text by default, the plain text version
giving you just the raw text with all tags and embellishments disabled;
but what would it do if you composed in HTML, switch to plain, added
some more words, then back to HTML? What formatting would (could) it
apply to the text added in plain text mode? I guess you'd have to select
it and manually apply a formatting style. :(