Thank you so much to Tim for his efforts!
I get the impression that the threat of discontinuing the Firebase component in App Inventor (with its excellent blocks for setting the ProjectBucket and .DataChanged) has forced you to redo a good portion of the work that someone probably already did 10 years ago, and to get very resourceful in finding workarounds (using JavaScript code in an .html file, a WebViewer, an event to detect changes in a WebViewString...).
Wouldn't that be a step backward? Especially since App Inventor's motto is precisely to teach people to program without the hassle of having to learn programming languages, and to make people with good ideas but not profesional programmers' lives easier with a "Low Code" platform.