@mckaygerhard in #677 was a PR to update Webhelper and Markdown plugins' Webkit, I took the changes from it in #746 and it got merged. #677 was merged but then reverted because the Webhelper changes didn't get approved/reviewed. So AFAICT support for newer Webkit in Webhelper plugin isn't done, or if it was, was done separately from those PRs.
I assigned @b4n, I'm sure he knows what's up.