Firefox lets you know when addon changes permission between versions. You are prompted to accept the new permissions before upgrading the addon. This has been helpful in weeding out addons that become too data hungry.
Yep switched a few months back last I heard about Stylish being bad, and never looked back. It works very similarly and you can import/export all your stuff so it's super easy to switch.
I guess there should be an addon that notifies users for any ownership changes to browser addons they use. Or is there?
[1] https://github.com/openstyles/stylus