I happen to also work on Firefox/Tor Browser's anti-fingerprinting work, so yea - we're trying to make improvements there too =)

Containers is a big Firefox feature (exposed through an Add-On) in this category too.

As far as Web Extension APIs, I don't know much about that, but if you have an API that would enable a use case that Mozilla doesn't have a bug on and haven't considered; you are welcome to file a bug explaining what you would like and what you would use it for, and the Web Extension team will consider it.