A few things:
- If you’ve been using Revo beta before this, make sure to clear your cache on the browser so the JS can reload.
- Your extensions may very well be causing issues. Do not use Firebug at any time, on any webpage, unless you’re debugging. Firebug (or httpfox) is known to be a vast memory hog and slows down JS apps significantly.
After that, if it still doesn’t work, read this:
http://modxcms.com/forums/index.php/topic,40188.0.html
And reply with the server/browser details.