My MINDSTORMS NXT-G software (educational & consumer versions) were working fine on my Mac (Snow Leopard) with Safari and Firefox, then recently the software stopped loading; there was now an error. So why? Well, it turns out that recently Firefox updated its software, the new 14.0.1 causes a problem with the NXT-G trying to access the Internet, even if you don’t use Firefox as your Internet browser; Firefox installed on your computer still causes a problem.
The solution (for now), I uninstalled the Firefox and just use Safari. Both versions of MINDSTORM NXT-G are working again.