The Nvidia website confirms that Nvidia 319.32 supports your GeForce GTX460, cf. http://www.nvidia.com/object/linux-display-ia32-319.32-driver.html
. So at least Nvidia does not seem to be the root cause.
"inxi -Fx" as a whole does not hold any hint that there might be a problem (driver problem or similar).
The very old edition of kernel v3.2 had already been mentioned. Updating it to 3.2.0-53 might "mysteriously" improve the situation, it might fail to do so.
You reported that Firefox closes all of a sudden. Question is what the popup messages state that you mentioned. The file /var/log/syslog might hold lines giving a hint what might be wrong.
Maybe switching off hardware acceleration in Firefox will stop Firefox windows from closing unexpectedly. (Edit => Preferences => Extras => tab "General" (or is it "Common"))
Sorry, but the inxi output alone does not ring any bell here.