KijijiCheck от Nathan Nesbitt

This is a simple add-on that stores information about previous cars you have looked at on kijiji, and provides summary information about the current car compared to old listings.

How to use:

1. Visit any car ad on kijiji.ca
2. Click on the add-on button

View the code
If you want to check to be sure that there's no funny business, the code can be viewed on GitHub.