Context ui broken

I cannot add/edit any conditions or reactions through the context ui. I allready had some path conditions and some block reactions, but after upgrading to 7.x-3.x-dev, I couldn't get anything done through the ui. I noticed a javascript error, which might cause the problem:

textarea.js:6Uncaught TypeError: Object #<Object> has no method 'once'

Please check the attached screenshot.