Firefox on iOS is not Gecko. Like all other browsers on iOS, it is a skin on the OS-provided Webkit. This is because fast JS execution depends on operations that are illegal for apps to access.
So we're talking about the M1 Macs, not iPhones - Firefox on Mac is Gecko. So the comparison of Webkit (iOS FF) vs. Gecko (Mac FF) is the comparison being made as you can download both if you want.
