you know this is a simple but good idea..
there are firefox plugins that will give you *previews* of sites just by hovering over a link, which would help avoid having to visit sites only to discover they are worthless,
BUT:
are there plugins that use some crowd or expert wisdom to basically put scores next to links based on the judged quality of the links (judged by experts, heuristics, or crowd voting, etc.)
Now that's a nice idea for a FireFox plugin.