Earlier quoted context omitted.
That isn't correct. Try the new mobile Firefox. Buying Pocket signalled that if you can take the right Mozillan to lunch, you can get an early exit. That did not solve the problem. It's still impossible to remove Pocket.
Yes, the latest mobile Firefox does make network requests. When Firefox updated, I got a "recommended by Pocket" section full of ads and click bait. I do not want that. And it's on about:blank just like when Chrome started capping up the blank page. I had to install a script to load an actual blank HTML page because about:blank isn't blank.
It's very chatty, annoyingly. Captive portal check on all requests that has to be disabled in about:config and a laundry list more. That config is scarily full of remote and telemetry based URLs also, but at least they are co figurable I guess.
An open source browser that just does what you want and no more seems like a dying hope.