FirefoxOS and ChromeOS are attacks on general purpose computing just as much as iOS is.
FirefoxOS and ChromeOS are attacks on general purpose computing just as much as iOS is.
If having restrictions on the runtime is your criteria for judging whether or not it's "general purpose" or not then every platform with a kernel fails because everything is subject to the restrictions it imposes.
Every platform has one "base" language - even rms' laptop can only run MIPS instructions; everything else must be compiled or interpreted. FirefoxOS just uses JS as its base language.
That being said, consumer devices need to be able to pass a sort of "slave test"; if your device can't hook up to a printer/scanner, or other peripherals, it is a device meant to enslave you in a digital jail.
Mozilla seems to be the best citizen thus far when it comes to user rights, and I wouldn't expect that stance to change much due to a different formfactor. this is still very much the same project JWZ founded.
Trying to divine somethings "general purpose" via just evaluating the runtime is murky and distracts from the core issue.
By the root standard iOS fails completely.
ChromeOS, Android and FirefoxOS all get middling grades in this.
But Firefox is in control of its sandbox. It has provided a lot of native API access that other platforms don't have.