It seems that you have Javascript disabled in your browser. We get that, really. However...
Javascript is required for the collapsing and expanding of objects and arrays - without that, this site is just a glorified JSON formatter (which is nice, too).
On top of that, if you have Javascript enabled, your JSON data is never sent to the server - everything is handled in your browser.
TL;DR: You're better off using this site with Javascript enabled.