Edit: I didn't scroll down far enough the first time, I see it now.

Looks fine for me, but I have disabled some settings that can interact badly with certain graphics cards.

Could you try turning off a few Firefox settings. I'm not sure whether you need all of these, but no single one seems to solve the issue for everyone.

You usually need to restart Firefox in order for these changes to take effect, so save all work first (e.g., mail you are composing, online documents you're editing, etc.).

orange Firefox button or classic Tools menu > Options > Advanced

On the "General" mini-tab, Browsing section, uncheck the first 3 boxes:

1. Use autoscrolling
2. Use smooth scrolling
3. Use hardware acceleration when available

If you OK that and restart Firefox, is the issue resolved?

Note that if some of the content getting chopped or striped is Flash video, there may be other issues.

There is a very large DIV container (67000 or more) on that page that may be causing the problem.
I'm not seeing this on Linux, but a Firefox Windows version running under Wine shows that problem after about 32700px.