Axel posted some great information in the MooTools User google group a while ago, sharing his expierence with Chrome 5. Recently, I ran into this very problem.
The problem was that a global variable defined by chrome itself. It was a global read-only variable, it was special. My plugin could not override it, so my plugin broke. It was the
media variable. Chrome sent back this error:
TypeError: Object #<a Media> has no method ‘play’
Google went completely against the mantra of reducing global variables and functions. I seriously hope this doesn’t happen increasingly as more browsers update their feature sets.