While tracking down an issue (ha!) with firefox 4 and PPC machines, I found this:
Unfortunately, PPC Tiger does not support OpenGL 2 at al (the really irritating part is that Intel Tiger does have OpenGL 2, and OpenGL 2 came out in 2004!).
Does SK have anything in it that wants OGL 2? Might this be why a G4 mac is so much worse than a microsoft windows system?
EDIT: REAL ICCKY:
Mozilla requires non-power-of-two texture sizes, which require OpenGL 2.
Does this mean that a 1024x512 display would have hardware acceleration, while anything else would not?
The minimum GPU specs feature cards that support up to OpenGL 1.3, So I'd say that's where the bar is. However, I bet only checking "Compatibility Mode" forces OpenGL 1.3, otherwise the game probably wants to use more advanced features.