Kimetrak (Who's tracking me) is an extension allowing you see at a glance what third-party domains are loaded from websites you visit.
You can access detailled statistics with a list allowing you to analyse what services are able to track you online, even if you use content blockers.
This tool can be used by internet users but also by publishers who want to know how many third-party domains are loaded from their websites. A precious information for GDPR/ePrivacy compliance.
The source code is available, under GPLv3 licence :