Inquisitor was Apple Safari’s only solid third-party search browser plugin back in the day. Yahoo acquired them back in May and then provided an upgrade in mid-August. Now, Yahoo has announced they have made this plugin available for Firefox and IE.
If you are running Firefox 2 or 3, you can download the addon over here. If you are running IE 7 or 8, you can download the plugin over here. I highly recommend you give it a try and check out some of the customizations I deployed on Inquisitor years ago.