Seems like a very narrow segment of people who:<p>- want to run custom JS from one tab in another often<p>- Wouldn't write their own extension to do it<p>But credit for OSSing your own tools :)
This seems very useful running a local first app in one of the tabs. Then using this, you can send requests to that app from anywhere and get your responses back where you requested from.
It looks like it might be any Chrome browser tab and not "any browser tab"<p>however since Firefox supports Broadcast channel API it should probably be theoretically possible in there.