Bug seen in current Fedora 22 - kernel 4.0.0-1.fc22.x86_64 , xorg-x11-drv-nouveau-1.0.11-2.fc22.x86_64 , xorg-x11-server-common-1.17.1-9.fc22.x86_64 , mesa-dri-drivers-10.5.1-1.20150314.fc22.x86_64 , libdrm-2.4.59-4.fc22.x86_64 .
If I view a page with a lot of vertical scroll in Firefox - say, a long article, or just a page with a lot of Disqus comments - after I scroll through quite a long way, the display of the page starts corrupting.
http://www.avclub.com/article/surely-you-cant-be-serious-oral-history-airplane-218043 is a good example: it starts corrupting around the "Into The Cockpit" section.
I can scroll up to any point above the 'corruption cut off' and it will display just fine...but if I scroll down below it, no matter how I do it (mouse wheel, scrollbar, keys, whatever), the rendering is corrupted.
https://www.happyassassin.net/temp/nouveau_scroll_corrupt.webm is a video demonstrating the corruption.
The video adapter is a 01:00.0 VGA compatible controller : NVIDIA Corporation G94 [GeForce 9600 GT] [10de:0622] (rev a1) ; Ben Skeggs has one of the same model.
Probably an issue with an X pixmap that is larger than the largest allowable texture size. X pixmaps go up to 32Kx32K, while nv50-family goes up to 4K (and nvc0 goes up to 8K).
If you're proficient with X tools, can you double-check that that's the case. (Not sure how you'd do it... xwininfo gives you info on windows, not pixmaps... you could look at an xtrace of it I suppose.)
I'm afraid I'd have no idea how to do that, sorry :(