I see that scrolling long pages with graphics such as The UK Daily Mail is much faster using the new Firefox for iOS9 than Safari.
Definitely the latter. If it was absent completely it would stop scrolling as soon as your finger left the screen and feel very artificial and unintuitiveIt's likely inertia scrolling in play, which isn't used in Safari (at least not to its full capacity).
Hard to say. Not sure it was really supported all the way at all, or perhaps quite a ways back at least.When did they first make this change to Safari? I've seen people talking about it since at least iOS 7. Very strange that they'd change something that was commonly the reason why people felt that both the iPhone and iPad felt like magic when they were first released. The current scrolling feels more like using like a slow scrollwheel when before it felt very 1:1 to your movement which is how the rest of iOS still handles it.