Sorry, I should have specified better. By "Linux" I meant the overall mix of Xorg and whatever display or GUI toolkits are in use, and instead of "graphics card

Sorry, I should have specified better. By "Linux" I meant the overall mix of Xorg and whatever display or GUI toolkits are in use, and instead of "graphics card", I should have said "graphics card drivers". If the card itself were having issues, I'm sure more than Firefox would have problems. Alternatively, I always hear about how "Linux has bad font rendering!" but since I'm not much of a font guy, I'm not sure if they're referring to how the fonts look, or some deeper part of the process which displays the fonts. I recently had to switch to the radeon (open source) drivers instead of fglrx (AMD's proprietary) drivers due to some incompatibility with a kernel upgrade. It makes sense that the problem would exist somewhere between Firefox and its use of those drivers.