It’s called SearchStatus.

After you have installed it, you’ll see it at the bottom of your browser on the right side. It displays a small PageRank and Alexa ranking status for any website you visit. Just make sure you restart your Firefox browser after you installed it so it can work.

If you have Firefox 1.5 and get this yellow popup at the top that says you have to enable downloads or something along those lines, then do the following steps:

1. Type about:config in the Address Bar and hit enter.
2. Type xpi in the Filter box and find xpinstall.enabled in the list.
3. Make sure its value is set to “true” (double-click will toggle).

That should do the trick and you’ll be able to download it properly. I find this plugin really useful, especially when you want to see your ranking for marketing purposes.