Hell, if you have a "clean" host/VM, I encourage you to install Firefox, start a packet capture, launch Firefox for the first time, then just sit and wait for 30 seconds or so -- not doing anything or interacting with it in any way -- before closing Firefox. Then, go take a look at your packet capture. I think you'll be quite surprised at all of the connections it makes...
This is really not the Mozilla Firefox I envisioned or expected way back when I first started supporting and advocating for it (when it was first announced!).