It could be very easily adapted to FireFox/Mozilla.
It's made for webmasters.
It gives you the PageRank of all the search results.
Because this tool is a bit "special", I'm sorry to not be able to give the sources. But if someone wants to know how it's done, send me a mail. I can send back the main part of the source (without the "special" part).
Download it at: PageRank Viewer