Today my Saturday project was to create a page that systematically tests the RESTful and CORS (XHR2) capabilities of browsers.
I've used synchronous (not async) calls to keep browsers from hammering my small server, so you'll have to wait for all 50 or so calls to complete, which takes a minute or two.
Later I'll clean it up and turn it into a table and, perhaps, store the results of visitors to create a version that only runs the tests if they haven't already been run on your browser.
If you would like to help, please contact me.
I'm coolaj86, I use google's mail system.