Firefox compatibility on scrolling and page title pinning

[haozhun]

Try browsing http://nodemanual.org/latest/nodejs_ref_guide/http.html in FireFox (This page is just an example. The problem exists on all pages.)

When scrolling down, section titles should pin to the top of the page when they are about to go above the current visible area of the page.

However, in FireFox, they will pin to the top of the page before they are about to go above the current visible area of the page. In fact, it sometimes disappear as early as when it is in the below half of visible area of the page. See these 2 screenshots.

This one is fine:

But if I scroll down a little more:

The section title "http.clientRequest" disappears from where it was and went to the top of page.

Instead, it should go to the top of the page only when I scroll down even more and the section title is about to go above the visible area of the page. (which is how the web page behaves in Chrome)

I use FireFox 18 on Mac OS X. But I guess this bug can be reproduced on any recent FireFox versions.