See: <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1293305">1293305 – Disable non-standard for-each on nightly-only</a> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/For-each-in_loops_are_deprecated">Warning: JavaScript 1.6's for-each-in loops are deprecated - JavaScript | MDN</a>
