User Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:21.0) Gecko/20100101 Firefox/21.0 (Beta/Release) Build ID: 20130511120803 Steps to reproduce: In console, execute JSON.stringify(performance.timing); Compare against performance.timing. Test against existing (Chrome and IE8+) results. Actual results: Returned "{}" Expected results: Should have returned serialized object.

https://bugzilla.mozilla.org/show_bug.cgi?id=727392 was a similar bug but unsure if this falls in the same vein.

The behavior is correct per spec. JSON.stringify only looks at own properties, but all the properties here are on PerformanceTiming.prototype. Chrome violates the spec by putting the properties on the object itself. IE violates the spec by adding a toJSON method on the object, last I checked, which is not in the spec but affects the behavior of JSON.stringify... See bug 760851 for details.