This might work on Firefox, but I doubt it, given it extends Chrome Dev Tools and Firefox doesn't have Chrome Dev Tools, it has its own very different dev tools.

I'm not sure what you mean by a "true" WebExtension; Firefox and Chrome addons are two types of webextension. They have a lot of compatibilities and generally share the same APIs on shared features, but each also has its own extra, unique features that will likely never be supported by the other.

> was the firefox quantum move a failure?

If you're choosing to define "failure" as not changing Firefox entirely to be a carbon copy of Chrome, then yes. Otherwise, no.