Firefox activates limited telemetry for folks who turn off the heavy stuff. While your firefox browser shows that no telemetry is taking place, the browser will silently send information about your browser, os, and other information to Mozilla.
Personally, the privacy implications don't concern me as much as a browser that is deliberately lying to and deceiving it's users (though I can certainly see how it can be privacy concern).
If someone wants true and total control over their browsing experience, neither firefox or chrome are a good choice (imo).
It's unfair to describe these as "installing random extensions without asking" because you would then have to admit that it's equally true of every new feature of every software program that is ever updated.
Chrome on the other hand removed that option years ago. Deleting Chrome Update's scheduled-task is my workaround.
I don't recall if extension updates can be disabled in chrome.
In general, I see firefox's point that using the system extensions to deliver autouodates and allow them to iterate more quickly. However, it also feels like whenever we see these extensions that they're something shady.