I known, many time ago, there was proposition to add page menu support to browsers. I do not remember, how it should work. But my idea is simple and probably different.
We currently have section tag and browser should support it, but before adding support of it, Firefox could gather anchors on page and generate menu for it. Anchor menu/map should be available near awesomebar.
I mean, Firefox should add possibility to navigate to any part of page with a tag with name set.