From command line, how to know which Firefox version is installed in windows/linux?

Question

I need to know which Firefox version is installed on my system from command line of Windows or Linux.

Answer 1

On linux (debian, lenny), you can use -v:

firefox -v
Mozilla Firefox 3.0.19, Copyright (c) 1998 - 2010 mozilla.org

(that was on a random server just now)