You are right. I ran a futuremark test on chrome, ff and safari (iphone 6) and chrome was the slowest BUT in terms of actual website loading, chrome was faster than FF. Although safari beat them all significantly!
Future mark scores:
Chrome:618
FF: 728
Safari: 2348
Actual website loading speeds were near instant on safari, followed by laggy chrome and incredibly slow FF.
While your test is exactly what is expected from iPhones, it says nothing about their performance on other devices.
Chrome and Firefox on the iPhone are not the same Chrome and Firefox found on desktop and android devices. Apple restricts apps that provide web browsing to use old and outdated versions of the native IOS rendering engine and JavaScript engine.
Future mark scores: Chrome:618 FF: 728 Safari: 2348
Actual website loading speeds were near instant on safari, followed by laggy chrome and incredibly slow FF.