Ability to embed Gecko as an alternative to Chromium Embedding Framework

[alexdelorenzo]

This would allow for Electron-like frameworks that work on top of Gecko and SpiderMonkey instead of Chromium via CEF.

It would also be good for embedding webpages in desktop applications. As it stands, CEF is the go to for this along with some WebKit-based options like WPE.

[SincereAlpaca]

@Jon are there any updates on this? This is extremely important to maintain an open web.