How does it work?

The toolbar icon Displays a color-coded badge with the number of requests served by CDNs. ORANGE means that external resources were served by a CDN, but the page itself was not. RED means the page itself was served by a CDN, and maybe also external resources. PURPLE means that resources on that page were served by multiple CDN.
The address bar icon (optional) Uses the same colors to represent the same information, except that it doesn't have a badge (because of API limitations). Instead, the color of the icon itself changes. This icon is only visible when relevant.
The popup It is displayed when you click on one of the icons. It lists the domains of the resources that were served by CDNs, and the number of detected requests by domain.
The options The options menu allows you to toggle detection of individual CDNs on or off. There is also an option to enable detection using heuristic patterns. Said patterns will detect edge nodes that the extension can't recognize as part of a specific CDN yet. Like all heuristics, it is not fail-safe, which is why it is disabled by default, but most of the time it should be a very good indicator.

Platforms detected You can find here a full list of platforms detected, and also ask for individual platforms to be added. Permissions requested

Access your data for all websites True Sight works by analazing the response headers of all requests, and there is no way to do that without asking for this permission.
Access browser tabs This one shouldn't be necessary (according to documentation) but, if I recall correctly, changing the address bar icon didn't seem to work without requesting this permission. Will probably check back, eventually.

TODO

Add patterns to detect a bunch more CDN.
Improve existing patterns where possible.
Improve my sloppy documentation.
Make the existing UI elements more visually appealing / useful.
Add some sort of accessibility option... if I can come up with something decent.

Visit the GitHub repository for more information.