Bug 1905322 disables them. This bug is for fully removing related code.

This includes the prefs
network.auth.confirmAuth.enabled
prompts.modalType.confirmAuth

Looks like these prefs along with the prompt code are good to remove. We don't have any plans on re-enabling.

Was speaking in regards with this offline and suggesting below

Looks like it is already disabled and we’ve haven’t received any complaints (not that I am aware of). Since desktop is doing it and other browsers on mobile(Chrome, Bing, Brave) don’t have it either, we are okay to remove it for mobile android too