FF broken in latest release w/ dom.webcomponents.enabled: true

[ebidel]

Visit http://www.polymer-project.org/getting-the-code.html in FF stable with dom.webcomponents.enabled: true. I tracked the console error down to Document.js:161 on a local build of the docs:

Not sure if we want to handle other browser's inflight implementations, but this one took me a while to
to realize it was the flag.

[dfreedm]

Yeah, I don't think they have entered and left document callbacks. You should probably just turn that flag off in firefox for now. Not sure if we can even test for correctness there...