This extension is based an example from MDN (https://github.com/mdn/webextensions-examples/tree/master/navigation-stats), but I've tweaked it and added some features. Firstly, the original extension only showed the top 5 most visited domains, so I added a button to see all the domains visited. I also added protocol tracking (HTTP/HTTPS) and display this information as a percentage of web pages visited that use HTTPS. I also added some CSS just to make the popup look slightly nicer.
The purpose of developing this extension is to familiarise myself with the extension ecosystem, specifically the web-extensions APIs.