When loaded and then scrolled using wheel, only the initially visible area is painted as expected, for the rest background color seems to be used. When using keyboard for scrolling, the page is painted correctly. The page needs scl3.mozilla.com VPN.
This is on 64bit linux, 40.0a1 (2015-04-26) nightly, e10s and apz enabled.
I can reproduce this but it's just a case of checkerboarding, not an actual APZ bug per se. If you wait a little bit the area gets painted. It's got a big load of SVGs which are apparently just slow to paint. If I disable APZ the page just doesn't scroll until it's good and ready so the behaviour when APZ is enabled is pretty much expected.
The page is repainted immediately once one scrolls using keyboard, but never when scrolling using wheel.
Hm, that's different from what I'm seeing then.
The behavior has changed recently, and painting seems to work fine.