History management support feature detection (WIP)

There have been several discussions on the topic: https://github.com/Modernizr/Modernizr/issues/733, https://github.com/Modernizr/Modernizr/pull/746, https://github.com/Modernizr/Modernizr/pull/891

Certain old browsers are returning a false positive, all leading to just using a UA sniff.
I haven't seen any attempts for an actual feature detect to rule it out.
This is a work in progress. Hoping this thread can spark some ideas.

Attempt 1:
http://jsbin.com/hexifuvi/1/edit
Update state; compare location; put state back.
Works, but touching the page's state is not desired.

Attempt 2:
http://jsbin.com/hexifuvi/5/edit
Run attempt 1 in an iframe.
Works, except in Firefox (https://bugzilla.mozilla.org/show_bug.cgi?id=777526)