Alas, I think it might be a while until torbirdy gets an update -- it involves somebody looking at Thunderbird 68 to see what new privacy invasive problems they put into it.
Maybe you, yes the person reading this ticket, want to take this on?
I would be interested in TorBirdy for Thunderbird 68.x, too. It is a great add-on (thank you very much for providing it); unfortunately, I have no experience in add-on development.
Similar situation here, it seems just now all Debian stable (Buster) installations have received the upgrade to TBird 68, leaving many many former TorBirdy users at risk, myself included.
How will Tails handle the situation? They've always relied on TorBirdy and they are now on Buster, maybe they can fix it in no time and make it available to all of us?
I just stumbled across this, too, since Thunderbird connects to mail provider(s) directly if TorBirdy was deactivated after upgrading to Thunderbird 68.x .
I guess the most important part of this comment was that one:
"I looked through the MailExtensions […] API of both Thunderbird 68, and the pre-release version, and didn't see any functions which would allow us to set the preferences set by TorBirdy"
So basically even if one would convert the manifest, the legacy extension would have no way to set the preferences needed to make Torbirdy work.
This is very sad and the options I see for the non-Tails Torbirdy usecase is
to check which are the preferences that still make sense with the new Thunderbird:
some issues have been mitigated by Tails' patches that were merged
some might have been mitigated by their total code rewrite
some new issues might have been introduced
to check with Thunderbird upstream directly if they are willing to implement those by default, or if they can provide an API endpoint into which an extension can hook into
manually change Thunderbird's preferences: basically what Tails will now do.
The two first options require time, communication skills and workforce, the latter is a more pragmatic "let's make it work" approach.
Torbirdy has been deleted from the Debian archive as no Thunderbird version that supports Torbirdy is shipped anymore in Debian. Tails has done work on modifying Thunderbird directly, and will upstream a part of their modifications, however, not enough to provide non-Tails users of Thunderbird with the same security as Torbirdy did. See https://redmine.tails.boum.org/code/issues/17281 and https://redmine.tails.boum.org/code/issues/17219 for more information.
I guess this all means that this ticket can be closed.