I know of only one addon for autocorrection and it doesn't address punctuation and it has no capability of recognising a related pair of glyphs.

I think the answer is "no".

With some hesitation, I'd say that if this is so important to you, then compose in Word and paste into Thunderbird. But to avoid the unholy mess of proprietary formatting code that would accompany a standard paste action, I'd say use "paste without formatting" and in all likelihood this would wipe out the curlies anyway.

Zenos: Thanks a lot for spelling it out. What I mainly wanted was a yes or no answer and I got it. No, it isn't important enough to do a Word paste and it doesn't sound like it would work anyway. But I do wonder why I'm forced to use the straight quotes. To me they're unprofessional and tacky-looking. I'm not using an old Underwood with a cloth ribbon. That's what those marks remind me of.

It's the new, flexible 21st century, Mozilla!

End of rant. Thanks again for your prompt reply.

I blow hot and cold between pretty text and plain text. In plain text, smart quotes simply isn't an option - unless you include that abysmal *nix practice of pretending that a back-tick is a reversed quote. An awful lot of linux-related documentation has this ugly `kludge', or even worse, ``kludge". In both cases, a simple 'standard' quote would have been the least bad option. (It's possible that some largely defunct rendering systems used in *nix systems might have done a switch at print-time to a nicer typographical symbol, much as Word automatically changes -- to —, but I have never met one.)

If you work in Unicode then you can insert them “by hand” and in this case I used my Clippings short-cut to insert them, since I don't care to commit their individual codes to memory. But it's not “automatic” as you initially requested.

abcTajpu will help you locate these characters, and Clippings or similar can be used to set them up as a keyboard macro. Both of these add-ons work in both Thunderbird and Firefox.