@Nasser When you view it locally, the pages are Mathematica notebooks, while in the browser, they are HTML pages. I'm not surprised that it makes a difference.

@C.E. ... and basically all non-text content on those web pages consists of statically generated images. Mathematica could frankly do some caching or advance rasterising of content on notebooks which are expected to be read-only and not manipulated, but I can see why it can be more hassle than it's necessarily worth...

@kirma Yes, and of course, in the browser war between Google, Apple and Microsoft, there is hardly any amount of hassle that they will spare, so performing as their browsers will always be a very difficult benchmark to beat.

@C.E. Frankly Mma could try harder in this regard, but with minor aesthetic improvement as a result it's probably not very high on the task list. Like, there could be a background renderer thread which would rasterize graphics for the notebook interface asynchronously and only if the user would explicitly touch those components or background renderer wouldn't succeed in the task ahead of time it would be done in foreground synchronously. Of course there are complications...

I found a workaround for the help page jerrky motion. It seems to happen when the page is first loaded. So as a workaround when I open the local help page, I would now do a quick scroll down over the whole content. This causes everything to be load. Then scroll back to the top and now start scrolling down slowly. Now there is no jagged or jerkey or pauses effect any more. The text is display smooth because everything was already loaded.

I started to notice this in latest versions of Mathematica. In old versions I never noticed this before.