Colored Folders

Z 5 z 5 gwězdkow pógódnośony

wót mmelcot dnja Awg. 17, 2021 · trajny wótkaz

This was indeed a nice add-on.

I was also disappointed to see it is not supported by Thunderbird > 73

But I just discovered that from Thunderbird 78, you can now set the folder color with a builtin functionality:
https://www.ghacks.net/2020/07/16/a-look-at-some-of-the-changes-in-thunderbird-78/