Error: Permission denied to access property 'toString'

The video embed field works, but if you check your page for js errors you might see this error:
Error: Permission denied to access property 'toString'
Without a line number.

This has to do with the youtube flash player itself. I found a fix here by using by adding ?html5=1 to the youtube link.

My own patch adds this, and now there is no more javascript error.