To disable the AI nonsense in the latest Firefox update, open a new tab and go enter about:config into the address bar. Enter the following and make them false:

browser.ml.linkPreview.enabled
browser.ml.chat.enabled
browser.ml.enable
browser.tabs.groups.smart.enabled
browser.tabs.groups.smart.userEnabled
extensions.ml.enabled
sidebar.revamp

Le dernier, sidebar.revamp, touche au panneau latéral (pas AI)