My technique is super low-tech. In my bookmarks bar, positioned conveniently below the site's favicon, I have a folder which is called "For Later". Into this folder I drop stuff I'll want to come back to at some point. Then (and here's the super part of my super low-tech claim), when I'm done with it I move it to another folder called "x" which I periodically delete and re-create.

This works everywhere with no extensions or anything, I use Foxmarks to sync the bookmarks themselves between machines (which you could skip if you only used the one machine), that's it.