WebSockets. It is a web-browsers own feature or it dependent goes from OS version?

I've interesting that question about WebSockets.

It's a web-browser own feature which develop and evolve by %WEB-BROWEER NAME% as they developers want, or this feature allowed to use dependent on OS version?

e.g. from windows 8, I can use this feature in JavaScript in IE and other browsers.

If feature goes from web-browsers, from which version it stable for Chrome, Mozilla, Opera ( feature supported by Opera 12)?