I thought Firefox enabled this automatically providing your graphics card drivers are up to date. If I force it enabled on my old GeForce Go 7600 all the text

I thought Firefox enabled this automatically providing your graphics card drivers are up to date. If I force it enabled on my old GeForce Go 7600 all the text comes out as black rectangles. I assumed Mozilla knew about these problems so only enabled it when they knew it'd be reliable. So maybe leave it to Mozilla?