Comment by skj

Pretty uncommon at tech companies, but it's entirely based on the company's policy. The company can fire you at any time (as long as it's not one of several specific bad reasons like racial discrimination), but it's the company that employs you, not your manager. So only the company can fire you.

Generally big tech companies don't give your manager the authority to blindly fire you, but only because that's a decision the company made.