IIRC there’s a workaround that involves symlinks and/or copying some json files into the Firefox folder under .var, but I don’t quite remember how it works.

I can swear I found a workaround for this, but I am no longer using the flat oak. I will dig through my notes and share a link if I can find it

Yes, as there is a bug report which for me seems unsolved.

Yes. Because it comes in two parts. The OS level package and the browser extension, if the extension can’t communicate with the OS level package then it won’t work.