If you were using the item my post referred to, it's not for Firefox. It's a widget for Mac OS 10.4. Double-click the downolad to decompress it, then double-click the widget icon to start the installation. It will ask you if you want to install it or not. If you choose to keep it, it will switch to Dashboard and give you the same choice again. Click "keep" and drag it to any convenient place on your Dashboard screen.

(If you were referring to something else and quoted my post inadvertently, I can't help you.)