Can `let`, `static` and `yield` still be used as Identifier?

[Gary Guo]

It seems that in JSFiddle running on Firefox, let declaration is disabled. So this cannot explain.

From: waldron.rick at gmail.com
Date: Wed, 31 Dec 2014 21:36:46 +0000
Subject: Re: Can `let`, `static` and `yield` still be used as Identifier?
To: alex at kocharin.ru; erik.arvidsson at gmail.com; nbdd0121 at hotmail.com; es-discuss at mozilla.org
  let = 1;  console.log(let); // 1
  var let = 1;  console.log(let); // 1
  let let = 1; // SyntaxError 		 	   		  
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