Comment 25 for bug 274575

The same problem seems to affect firefox-3.5 as well.

Option "NoAccel" did indeed seem to make the problem go away, but also gave me a warning about "low graphics mode" and reverted my dual-monitor setup to a mirrored configuration. Which could be expected behavior, for all I know. Either way, it suggests that the X server configuration is indeed a factor.

I very much doubt this will turn out to be Firefox's fault, though it doesn't seem to me that any number of xorg.conf experiments can prove it isn't -- Firefox could conceivably be doing something wrong that usually happens to work but occasionally causes problems under complex circumstances.

I'm tempted to try to put together a repro case for this bug that doesn't involve Firefox at all, but I evidently don't have a clear enough idea of how Firefox actually renders images to have succeeded in reproducing the artifact thus far. I've got a toy program here that pops up a window containing a scaled raster image on a white background (using cairo, which I have a vague idea that Firefox might also use), but of course it renders without any artifacts. Ah well.