I'm not a tech guy who knows how these things work, so forgive this question if it's really obvious. Many of the extensions I've seen (Share to Facebook, Instasafari, etc) already have existing bookmarklets. What's the difference between a bookmarklet and an extension? It seems like the bookmarklet would be better resource-wise because it's only used when it's needed whereas an extension (I guess?) runs with the browser itself. Am I way off on that?