fix FF contenteditable backspace bug.
https://github.com/yui/yui3/issues/1376
tweaks per YUI team advice on pull request.

https://github.com/yui/yui3/pull/1502
tweaks per YUI team advice on pull request.

https://github.com/yui/yui3/pull/1502
tweaks per https://github.com/yui/yui3/pull/1502/files#r8857828
tweaks per https://github.com/yui/yui3/pull/1502/files#r8852815
Merge remote-tracking branch 'joecomotion/editor-para' into dev-master
[Editor] : Build.
[docs] Fix trailing comma in GH Contributors mocks
Merge branch 'dev-master' into dev-3.x