Composer no longer inserts emoji correctly

[ara4n]

I end up with both emoji-one and plain emoji when i use the macOS emoji picked (ctrl-cmd-space) to insert a 👍on FF in Slate in MD mode:

[jryans]

(Verified this is not a regression from /app at least, same behavior there.)

[lampholder]

I think this is a dup of #7347