And I agreed that this is not “pure” Vim.
But I did need to find a compromise. There is little point in having an “insert” mode, like Vimium does, since I am targeting a very specific website and not overriding any existing shortcut (AFAICT). If you think it's important to you, I might consider implementing custom key bindings so that you can use with “pure” Vim shortcuts!
Regarding the scrolling, it could be two things:
1. I do not update the address bar on every key press, to avoid some kind of rate limitation I encountered when I did so initially. Instead, there is a very short delay so before it happens. But the viewport should still scroll immediately. 2. If it's smooth scrolling, there is actually a toggle you can change in the extension settings. If you still have the behavior without smooth scrolling, I would be curious to know more, to see if I can make the experience more pleasant.