Rated 4 out of 5 stars

Great for supporting Thunderbird latest version instead of the original plugin.

But, on v3.2.4, it changed style CSS setting to use its own one.
Styles for the original ver. is not inherited. Gee...

And, on this ver., syntax highlighting is not working, does it?

Now it looks having several problems on CSS settings.
Unfortunately, unwelcome update...

This review is for a previous version of the add-on (3.2.4). 

Yes, syntax highlighting is broken in 3.2.4. Version 3.2.5 will have fixes for that and several other issues.
This is a new addon with its own ID, so it it not able to access the extension storage from the original Markdown Here.
If you modify the CSS to suit your taste in settings, your changes will be kept on future updates. If that's not the case, it's a bug.

Rated 5 out of 5 stars

This was the one killer addon for Thunderbird (well, together with Muttator). Thanks for bringing it back :)

This review is for a previous version of the add-on (3.1.1). 

Rated 5 out of 5 stars

Amazing, works well.

However, the "Have full, unrestricted access to Thunderbird, and your computer" seems exaggerated, please request only required permissions and this would be perfect. (edit: see answer).

Also, it keeps asking (edit: not anymore) me "It looks like you wrote this email in Markdown but forgot to make it pretty. Send it anyway?", even when I just did make it pretty.

Edit (reply):
Thanks for the explanation on the permission, fair enough. Also I do not have false positive anymore, I don't know why, but good. So all good, thanks for the work.

This review is for a previous version of the add-on (3.1.1). 

I updated the description with the reason for the "unrestricted access" permission. Mail extension APIs are evolving, and my expectation is that the missing API or one that accomplishes the same thing will be added in a future Thunderbird version.

I have not had many false positives with the markdown detection, but not too many. If you have a sample message that incorrectly triggers the notification, please file a bug on the Gitlab page.

Rated 4 out of 5 stars

Nice. But it seems that footnotes are not supported, or are they? That is, something like https://www.markdownguide.org/extended-syntax#footnotes

Also, a keyboard shortcut to toggle rendered/raw views would be very appreciable.

Otherwise, nice job, thanks.

This review is for a previous version of the add-on (3.1.1). 

Ctrl+Alt+M is the default hotkey. You can change it in the preferences.

Footnotes... not really. You can try this suggestion I copied over from the original Markdown Here: https://gitlab.com/jfx2006/markdown-here-revival/-/wikis/Tips-and-Tricks#footnotes

Rated 5 out of 5 stars

Thank you very much for the time and effort to resurrect this very useful add-on. Now we can once again send nicely formatted email messages containing code.

This review is for a previous version of the add-on (3.1.1). 

Rated 5 out of 5 stars

Thanks a lot for this, I was really missing it :)

This review is for a previous version of the add-on (3.1.1). 

Rated 5 out of 5 stars

Love it! Makes composing emails much faster, and works nicely with new TB

This review is for a previous version of the add-on (3.1.1).