Comment 28 for bug 765813

It's interesting that when pageflip is active, it's always vsync-ed, so enabling/disabling vblank_mode just enables/disables flickering, without real effects on the framerate.

IE with pageflip on and vblank_mode=0, the fps can jump between 30 and 60 fps because my machine is too slow but there is not any flickering to see.