Mozilla is always experimenting with ways to improve Firefox. Granted, few of these experiments actually make it into Firefox it seems, but that's not stopping anyone from Mozilla from piling them on. Mozilla's Prospector series of experiments is perhaps the best example of this.
There have been several interesting features, tacked on in the form of extensions, and even a few radical revamps of the UI. But none of them have led to any change in Firefox.
No matter, here's a new one, it's called Site Suggest, can you guess what it does? Spoiler alert: it suggests sites. Specifically, it's a new tab page modification that adds some recommendations based on your browsing habits.
It replaces the last thumbnail in the new tab page with suggestions. These suggestions are based on your interests, but there's no tracking data being used or stored. What's more, the suggestions aren't very good, this is just a proof-of-concept.