User blog comment:Sarah Manley/New Editor Scheduled for Sitewide Release/@comment-161139-20110908205123

There's a MAJOR (literally wiki-breaking) issue when modifying site javascript. If you accidentally break Common.js it seems to break the editor as well... meaning you can't even edit Common.js to fix it. The editor NEEDS a fallback option to save pages that does NOT rely on javascript.

You can always roll things back to a prior version, but it's still very much wiki-breaking.