Issue 6391 - Allow running the browser unit tests with Firefox

test/runners/firefox_process.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-/* eslint-env node */
-
 "use strict";
 
 const {Builder} = require("selenium-webdriver");
 const firefox = require("selenium-webdriver/firefox");
 require("geckodriver");
 
 const {executeScript} = require("./webdriver");
 const {ensureFirefox} = require("./firefox_download");
 
-const FIREFOX_VERSION = "60.0b4";
+const FIREFOX_VERSION = "56.0";
 
 function runScript(firefoxPath, script, scriptName, scriptArgs)
 {
   let binary = new firefox.Binary(firefoxPath);
   binary.addArguments("-headless");
 
   const options = new firefox.Options()
         .setBinary(binary);
 
   const driver = new Builder()
         .forBrowser("firefox")
         .setFirefoxOptions(options)
         .build();
 
   return executeScript(driver, "Firefox", script, scriptName, scriptArgs);
 }
 
 module.exports = function(script, scriptName, ...scriptArgs)
 {
   return ensureFirefox(FIREFOX_VERSION).then(firefoxPath =>
   {
     return runScript(firefoxPath, script, scriptName, scriptArgs)
-      .then(result =>
-      {
-        return result;
-      }).catch(error =>
+      .then(result => result)
+      .catch(error =>
       {
         throw error;
       });
   });
 };