Rated 5 out of 5 stars

le mkaulke ar DFómh. 20, 2023 ·

Does not work in thunderbird 115.3.3. No effect on message pane.
Update Oct 20: Followed the developer's instructions, and now the extension works. Might be a miracle ... but hey,

Léirmheas ar leagan níos sine den bhreiseán seo (3.6). 

le Juraj Mäsiar (Forbróir) ar DFómh. 20, 2023 ·

Hello,
Thunderbird sometimes breaks addons...
You can try to uninstall Darko, restart Thunderbird and install it back. That may help.
Alternatively, there is another (probably even better) dark mode addon - Dark Reader which may work.

Best Regards,
Juraj Mäsiar