Intent to ship: Unprefixed Fullscreen API

[Xidorn Quan]

As of Firefox 64, I intend to turn on unprefixed Fullscreen API by default on all platforms. It has been developed behind the full-screen-api.unprefix.enabled preference.

Bug to turn on by default: https://bugzilla.mozilla.org/show_bug.cgi?id=1269276

Unprefixed Fullscreen API has been enabled in Nightly since Firefox 47. We once attempted to ship it at that time, but failed because of some webcompat concerns which happen only when unprefixed Fullscreen API is present. Since then, the spec has been revised to address some of the issues, but some of them were not fixable from our side, so I hoped to have other browsers do coordinated shipping with us.

After years, Chrome / Blink eventually caught up the spec, and it reached a point that they are attempting to ship it now. I think this is the best chance ever we can have unprefixed Fullscreen API actually available on the web. Chrome will ship it in Chrome 71 which reaches stable on Dec 4, and Firefox 64 will reach release on Dec 11, so it's roughly the same time frame.

Notably, there are two feature changes since our last attempt to unprefix Fullscreen API:
1. Fullscreen related events are now dispatched to element when it is still connected in the same document, which matches other browsers' behavior and provides better modularization opportunity.
2. Element.requestFullscreen() and Document.exitFullscreen() now return Promise which gets resolved when fullscreen change finishes.

I'd also like to deprecate the prefixed Fullscreen API, but probably we should do that only after unprefixed Fullscreen API reaches release.

- Xidorn

[Andrew Overholt]

Congrats on getting this far, Xidorn! I know it's been years of work by you
and others.

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[Chris Pearce]

Great work, happy to see fullscreen finally move to unprefixed!

[amine...@gmail.com]