Mozilla has been in hot-water in the past for silently installing extensions and more. But to your last comment (i.e. users can change their search engine whenever they want), consider the 'tyranny of the default'. Most users will not make changes to their browser out of the box. Most users frankly do not know how, or even know that they ought to in some areas.
When you install Firefox, and fire up that first session, your keystrokes in the address bar are sent to Google. There is no warning, or permission prompt. The same would happen if you accidentally pasted-in your social security number, or some other sensitive information—it gets sent right off to Google. It was this type of behavior, in part, that led independent researchers at Trinity College to grade Firefox lower than Brave in terms of out-of-the-box privacy: https://www.scss.tcd.ie/Doug.Leith/pubs/browser_privacy.pdf. In fact, Brave was found to be in its own class as the most private browser tested.
When you install Firefox, and fire up that first session, your keystrokes in the address bar are sent to Google. There is no warning, or permission prompt. The same would happen if you accidentally pasted-in your social security number, or some other sensitive information—it gets sent right off to Google. It was this type of behavior, in part, that led independent researchers at Trinity College to grade Firefox lower than Brave in terms of out-of-the-box privacy: https://www.scss.tcd.ie/Doug.Leith/pubs/browser_privacy.pdf. In fact, Brave was found to be in its own class as the most private browser tested.