This does have the effect of making Firefox buggy and not showing the content at the top of a page before you scroll down and up again. Which only works on sites you can scroll on.
What? If I'm sliding physical objects around, I normally expect them to just stop abruptly if they hit something.
...and indeed, that's what scrolling in UIs also did for a very long time, accompanied by a very clear indication in the scrollbar that you've reached the end:
http://www.functionx.com/vs2010/forms/scrollbar2.gif
The "designers" happened, and all of a sudden scrollbars turned into these horribly thin and imprecise roundish blobs that are far worse for indicating where exactly you are, and in particular, whether you've reached the end.
and frankly, any personal opinion doesn't matter in this case - it's a non issue. Just give us options to customize it to our preferences, and don't try to force others to follow The One True Way.