by Realraven (Axel Grude) (Developer) on Oct. 31, 2020 · permalink

Let's take one step at a time - we are still working on Thunderbird 78.* release and the max version doesn't currently allow higher numbers. This is because we simply do now know whether 80+ versions will permanently allow "mail extensions using experimental APIs" - which ius currently the only way to pull off all our functionality.

APIs for doing a lot of the advanced stuff need to be written first so that we can convert to a full mail add-on in the course of the year. In the meantime, try to install

https://github.com/RealRaven2000/QuickFolders/releases/tag/5.0pre116

no guarantees that it works with beta versions!