Thanks for reporting. Sadly I don't think Oracle is putting much attention to keeping the embedded browser current. I'm looking into serving local previews from an embedded web server (Jetty) so we don't have these JSON loading warnings which is now affecting all browsers.
I can't report anything, or add a post to that existing report - only OpenJDK Authors have posting privileges, and to get that, you have to jump through all kinds of hoops (including already being a project contributor).
The other bugs (cursors, borders) are fringe cases that can be ignored.