Hi DavidR,
The analogy here is like that with server software. You preferably for security reasons do not give away the version number to give not too much away for a hacker to be exploited, well seen as with browsers users could know for instance that IE5 is less secure than IE9. Best policy is like Chrome has it update automatically to the latest most secure version and do not let the user interfere or the browser developer. Do not know where Mozilla got this plans from?
polonus