That's strange... I don't see any weirdness.. Have you tried other browsers to see if this issue is an application issue
I think I figured out the problem. This is the only artifact I'm getting now on CM10.1, and you can see it by going to Youtube and picking a video and zooming in with pinch zoom. This is what it looks like:
Since the scroll lag I was getting before is all gone, along with some other launcher and lock screen bugs, I'm gonna chalk this one up to Flash being incompatible with 4.2.x. I don't see this wierd corruption on my 4.1 ROM's, only on CM10.1, but I'm guessing since all the other artifacts are resolved that this isn't a corruption from the drivers but from Flash buggyness.
If someone else could confirm that you see these artifacts on Youtube, with Flash player not installed, then we can see for sure whether it is that or not. I already wiped and returned to my TouchWiz ROM otherwise I would. The thought just came to me as I read your post lol
Update: I figured I'd save everyone the trouble and just test it myself and yep my suspicions were confirmed. The last remaining artifact I was seeing was a fault of Flash not being compatible with 4.2, and not the GPU drivers itself.
I went back to the exact same page that I took those screenshots on and this time I didn't have Flash player installed, bingo perfect rendering no artifacts. Well I guess this is a mixed feeling type of thing. I love knowing that CM10.1 is no longer experiencing artifacts compared to before, but also saddened to see an almost impossible to avoid killing of Flash player on Android
sad face is sad.