check fx version is valid

gistfile1.php

<?php
    function isValidFirefoxDownload() {

        if (!isset($_GET['product'])) {
            return false;
        }

        global $config;
        $versionDetails = (int) str_replace('firefox-', '', $_GET['product']);

        // If $versionDetails == 0 it means that the version number is a
        // potentially valid keyword such as latest, stub, beta...
        $majorVersion = ($versionDetails == 0) ? LATEST_FIREFOX_VERSION : $versionDetails;

        // List of validity checks. Can be extended. Boolean values.
        $valid = array(
            isset($_SERVER['HTTP_REFERER']),
            (bool) strstr($_SERVER['HTTP_REFERER'], $config['server_name']),
            ($majorVersion < (int) LATEST_FIREFOX_VERSION) ? false : true,
        );

        // We don't want to redirect requests for ESR or Thunderbird
        if ((bool) strstr($_GET['product'], 'esr')
            || (bool) strstr($_GET['product'], 'thunderbird')) {
            return true;
        }

        // If we have failed constraints, a filtered array will be smaller
        if (count($valid) > count(array_filter($valid))) {
            return false;
        }

        return true;
    }

    // Redirect non-latest versions of Firefox download requests (Bug 887940)
    if (!isValidFirefoxDownload()) {
      header('HTTP/1.1 301 Moved Permanently');
      header('Location: /firefox/new/');
      exit;
    }