You're mixing up macOS and iOS. The user is referring to Firefox on a MacBook Pro where there are no restrictions on choice of rendering engine. You're also mi

You're mixing up macOS and iOS. The user is referring to Firefox on a MacBook Pro where there are no restrictions on choice of rendering engine. You're also mixing up symptoms. If all browsers were forced to use the same rendering engine, you'd see little divergence of CPU/energy usage. The user is seeing a wild divergence—which is what you might expect when browsers are using different rendering engines. You're also mixing up talking points. People have accused Safari of being many things, but being profligate with CPU/energy usage is certainly not one of them.