A site claims that there is a "fundamental problem" with Firefox updates using the OS X operating system.
Linux and Windows operating systems are affected too.
Paul Sture says that if you run as a non-admin user on OS X, Firefox grays out the check for updates menu item and doesn't automatically tell you when security updates are available.
Firefox, he says, only allows Update Checking when you have write access to the Firefox application although most people do their daily work on a non-privileged account.
He says he's pointed out the flaw to the Secure IT Foundation.
There's more details here .