Rated 5 out of 5 stars

This add-on was so nifty and useful, it made me sign up just to post the review :-)
Simple, does what it's supposed to be, that's what it takes to get 5 stars.

My only missing feature: add support to use the app via the search engine bar, for tracking numbers that aren't in a web page.

This review is for a previous version of the add-on (2.4).