I would really like Firefox to implement granular permissions per extension. So, if I can choose to not give this extension permission to talk to external programs. And hopefully the extension authors wrote it in a way that it degrades gracefully.
If you don't install the companion program, this permission won't do anything.
It does not allow the extension to run arbitrary programs.
I think these permissions cannot be optional: https://extensionworkshop.com/documentation/develop/request-...
(Not sure though, I haven't worked with optional permissions for my extensions yet.)
Another thing I'd like is for Mozilla to not be able to deactivate extensions remotely.