Developers evangelized Android and Chrome in their early days - created the monsters. People making Chrome only sites are feeding the monster. Instead of Kozmos shutting down, the best revenge would making a firefox extension and getting their users to switch.
Or even Edge. Their new Chromium based builds are Chrome compatible and have their own store.
I have been working on an extension that uses Chrome's Debugger API, lots of tab / network related APIs, and DevTools. I spun it up on Edge the other day and...it just worked. Everything worked.
I can't say the same for firefox. They do a good job bringing over some extension APIs, but I find it severely lacking for my use case.