There’s these programs you really like, but they might have these little inconveniences which are too small to really matter, but still kind of annoy you. Well HTML-messages in thunderbird are on such thing. Usually I don’t want HTML-messages, but sometimes not limiting yourself to unformatted UTF-8 comes in handy (for me basically when writing in arabic, so I can have a bigger font-size and a natural right-alignment). Now, the only option to switch between HTML and plain text composing was to use the preferences dialog. Click, click, click annoy click etc.—sucks!
I just discovered (by accident), that if you hit the NEW or REPLY button with SHIFT pressed you can compose a mail in HTML for just this message. I wish I knew that earlier.