One of the most powerful tools in all of the modern desktop browsers is the ability to add extensions. Extensions allow the browser to do things that it can't do on its own - everything from simple tasks to advanced options. When it comes to desktop extensions, the limits are generally left up to the mind of the creator.
Up to this point, extensions haven't been all that widely adopted in the mobile world. In the cases of browsers that actually have extension support, the experience lacks much to be desired and it just doesn't compare to what desktop browsers have to offer.