I just deployed an update to the site - There is now an option to update existing accounts to HTML5 (at the top of the My Games page). All newly created accounts will use HTML5 by default.
I also updated the engine to fix a few bugs:
* Cursor misaligned in editor for some screens should be fixed
* Run & Jump behavior bundle tweaked
* Y scale issues (not scaling when only Y is adjusted, not scaling to 100%, and "pancakeification") have been resolved
Please let me know if you encounter any issues with this release.