On bugzilla, the main content area has a gray background, but since setting gfx.content.azure.enabled I've noticed it doesn't always load properly. I don't think this has been a problem on my Mac (both are running recently Nightlies).

Here a similar problem is seen in the footer. When I moused over "My Requests" and "Preferences" the background color was filled in for them, but it remained otherwise missing. Note that at the rightmost edge the dark gray color is slightly bezelled (or whatever you call it), which suggests maybe the background color block is shifted down a bit. Scrolling up and down changes whether the background is missing or not, and how it is missing.