If they do this, I will uninstall Firefox and start recommending some other browser. Mozilla has really sunk in my eyes the last couple of years but this is the final spike in the coffin for me.
On Windows, Microsoft Edge is of course a lean and capable browser, but the OS itself is also collecting telemetry on you at all times, including browsing habits.
Hopefully someone will fork Firefox for Windows/Mac/'nix and strip out all the telemetry and data gathering bits, otherwise there's not much choice left for a privacy focused, full featured, fully supported browser on all platforms.