Greasy Fork is available in English.
YouTube Center contains all kind of different useful functions which makes your visit on YouTube much more entertaining.
< Rückmeldungen auf YouTube Center
Of course this cannot be done in Javascript. Use Caffeine: http://www.webupd8.org/2015/01/caffeine-app-gets-its-indicator-back.html
screensaver off
Please make prevention screensaver on ubuntu