The `FullScreenEnabled` preference is not meant to be an internal debugging toggle, so should be labeled as `embedder`. This patch is a partial revert of 259054@main.
<rdar://104830750>
Pull request: https://github.com/Webkit/WebKit/pull/9343
Committed 259586@main (c4d95cca9a1f): <https://commits.webkit.org/259586@main> Reviewed commits have been landed. Closing PR #9343 and removing active labels.