The problem

Sometimes I run across a document or online book, the length of which requires me to read it in chunks. In the past I've simply used the excellent Instapaper service, to create a feed of items I'd like to read at a later time. Lately, however, that system has broken down. Behold, the RDF Primer, a single 80-page document that I've had to take multiple breaks from reading!

Sadly, it's not possible to keep track of exactly where I'm at in the document, meaning I have to remember where I was at at all times.

What I need

All I really need is a way to keep track of things that I want to continue reading at some later point. Whether it's something I've just stumbled across and don't have time to read immediately, or it's a treasure I have to pull myself away from for a while, I need a way to get back to that exact spot later on.

I don't need to keep track of a page I visit frequently; either I'm keeping abreast of its content in my feed reader, or it's a service that I post things to frequently, which means it's already in my history (e.g. the Tumblr dashboard is d[tab][enter]).

A solution?

I've looked for a Firefox extension that would let me bookmark my exact spot in a page, but I haven't found one yet. As I use my feed reader as my go-to spot for things that I want to read, it would be nice to have an extension that can jump to precisely where I left off and integrate with my feed reader.

One day I'll have that technology. I hope.