The extension schemas have many definitions that are copied from Chromium and marked as "unsupported".

I did some spot checking:

• processId in webNavigation API is not needed to uniquely identify frames and was deprecated / stubbed in Chrome's webNavigation API during the implementation of site isolation support for extension APIs.
• downloads.drag method was removed from Chrome due to security concerns. We have no reason to implement this method.

We should go through the schemas and remove unsupported values.

https://searchfox.org/mozilla-central/search?q=%22unsupported%22%3A&case=false&regexp=false&path=extensions/

Would be nice to reduce per-process memory overhead for Fission.

This bug was lurking in my head after the triage meeting. Lets be sure that isn't used for part of producing docs for mdn. I like a source of truth handy since MDN lags or sometimes misses some items. If we want to reduce memory, strip unwanted stuff out of the schema when we parse it in Firefox.

Tomislav says this bug doesn't need to block Fission MVP.