Fix bug 1312228: Stop tab loading animations when not needed
Fix bug 1312228: Stop tab loading animations when not needed

Also prevents high CPU usage

jotes/pontoon,mathjazz/pontoon,participedia/pontoon,participedia/pontoon,mathjazz/pontoon,jotes/pontoon,mathjazz/pontoon,mastizada/pontoon,jotes/pontoon,mozilla/pontoon,mozilla/pontoon,mastizada/pontoon,mozilla/pontoon,mathjazz/pontoon,participedia/pontoon,mozilla/pontoon,mathjazz/pontoon,participedia/pontoon,mastizada/pontoon,jotes/pontoon,mozilla/pontoon,mastizada/pontoon