Created attachment 8762087 [details] proof of concept User Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 Safari/537.36 Steps to reproduce: Adding a breakpoint in an onblur event causes the current tab to become unresponsive (unable to click anything in the tab, including the Click To Resume (play) button). When the tab and/or browser loses focus, the tab will then become responsive again. In the attached example, adding a breakpoint at line 10 exhibits the behavior. Actual results: The browser tab hangs. Expected results: The browser tab should not hang.
At first glance, this sounds like a nested event loop problem.