In Preferences/Composition/General/HTML, set the font to Georgia, and in Preferences/Display/Formatting/Fonts & Colors/Advanced, set the Proportional box to Serif as well as Serif to Georgia. Uncheck 'Allow messages to use other fonts'. Repeat for Fonts for: Other Writing Systems. Does that produce the desired display?

Thank you very much for writing. No, that doesn't change anything. (I didn't see the "Other Writing Systems.")

After about 20 years now, I'm going to give up and quit using Thunderbird I guess, and switch over to Mac Mail — mainly because of typographic issues (default sans-serif now, plus no smart quotes).

So now I need to know these things:

How do I get Thunderbird to stop downloading emails? I want to read emails only in Mail. Do I have to delete my Thunderbird account entirely?

I have a client to whom I email stories I've edited in Word, and because Mail adds space between the paragraphs, I would like to be able to SEND ONLY to this client using Thunderbird. If that's not possible, I hope to find out how to stop Mail (or Word) from adding extra space between paragraphs that's not visible when editing in Word ...

Sigh.

'Other Writing Systems' is available from the Fonts for: drop-down, which defaults to Latin. If you don't adjust the settings for OWS, you may not see any difference:

https://support.mozilla.org/en-US/questions/1239826

If it's a POP account, uncheck the relevant boxes in Account Settings under Server Settings. An IMAP account will download mail as it arrives at the server, so if you don't want this, Remove it through Account Settings/Account Actions.

The best way to send Word files is as attachments. If you must copy Word content into TB messages, use Paste Without Formatting (Ctrl+Shift+V).

Thank you very much! I found "Other Writing Systems" and fixed that, and now all messages have serifs, so far.

Haven't gotten to the POP bit yet ...

I'm on a Mac, so when I paste a Word doc without formatting (Command Shift V) into MAIL, 2 extra blank lines get added between paragraphs (beyond the one blank line I want there). Same thing happens when I use the simple Command V.

When I paste a Word doc into Thunderbird using either method, everything is correctly spaced and sized.

I would eventually like to switch to MAIL permanently, but will have to solve the Word pasting thing first, because that's how my main editing client likes to receive it.

Until then I'll have to stick with Thunderbird for mailing to this client, which I guess means I'll have to keep RECEIVING emails in Thunderbird too. And I would be happy enough with that IF ONLY Thunderbird could automatically make smart quotes ...

Sigh.

There is a smart quotes add-on that can be installed in TB 60, but only the quotes-converter button works, as mentioned in one of the reviews.

https://addons.thunderbird.net/en-US/thunderbird/addon/smart-quotes/

To install, first open Preferences/Advanced/General/Config. editor and double-click the preference extensions.strictCompatibility to false, OK to close Preferences.