Hello. I'm pretty much going crazy over here because my mac has never acted like this before. I can't copy paste, open applications, install applications (it says : "file name" could not be saved due to an unknown error. Try saving to another location." When I go to firefox settings, it will NOT let me change where I save my files to. Chrome/Safari won't even open, firefox is the only working browser. (Interestingly, this all started when I downloaded Firefox 4 beta...) Any help would be greatly appreciated.