I don't use 3D view but I've used Jesse Rudderman's topo bookmarklet[1], which is conceptually very similar, for years. It's more useful in IE so you can see what tag IE is failing to close but it's useful for getting a quick feel for unfamiliar markup when doing Greasmonkey hacks and the like.

[1] https://www.squarefree.com/bookmarklets/webdevel.html