Browser extensions

A browser extension can generally see and change everything you see and type in your browser, including your email and your bank.

That is not a flaw, it is how most of them do their job. The awkward part is that extensions get sold. Somebody builds something useful, gathers a few hundred thousand users, and then sells it to a company you have never heard of, who pushes an update. You are not asked, because you already trusted it. So the one you carefully checked two years ago may not be the one running now. Keep the number small, and remove the ones you no longer use.