Package Tracking Extension
Simple and to the point. I like these types of extensions. I always want to track my NewEgg.com shipments, so here is THE extension for making sure you know where your package is at, regardless of has it.
The Package Tracking extension takes a highlighted tracking code (that you highlight) and uses the context menu (right-click) to send the selected text to UPS, USPS, or FedEx to see where your package currently at.
The extension does what its supposed to do and it does it well. This type of functionality would be nice if it was incorporated into Firefox with version 2.0.
Oh, and by the way, for those who are adventurous, they also have a .NET Framework DLL available for download if you program in .NET. Another feather in their cap. Multiple ways to access the tracking functionality without additional programming.