Подскажите пожалуйста, существуют ли у firefox ключи, с которыми можно запускать программу из командной строки windows. Т.е. передать при запуски ссылку, параметры прокси или что-то еще.

Вот ключи, используемые в линуксе. Возможно и в windows они работают.

Выделить код

Код:

-height value
              Set height of startup window to value pixels.

       -h, -help
              Show summary of options.

       -installer
              Start with Mozilla 4.x migration window.

       -width value
              Set width of startup window to value pixels.

       -v, -version
              Print Firefox version.

       -no-remote
              Don’t connect to a running firefox instance.

       -a application-id
              Check for a running Firefox started with the specified application-id.  When firefox is invoked for  the  first  time  with  a  particular
              application-id,  a  new  Firefox  application  is  started;  subsequent invocations of firefox with the same application-id will cause the
              already-running Firefox to bring up a new window.

              The default is -a firefox.

       -CreateProfile profile
              Create profile.  Implies -a firefox--profile, or -a default if profile is default.

       -P profile
              Start with profile.  Implies -a firefox--profile, or -a default if profile is default.

       -ProfileManager
              Start with profile manager.  Implies -a with a fresh unique application-id.

       -UILocale locale
              Start with locale resources as User Interface locale. By default, it is guessed from environment and available locales for Firefox.

       -contentLocale locale
              Start with locale resources as content locale. By default, it is guessed from environment and available locales for Firefox.

       -new-window URL
              Open URL in a new window in an already running Firefox process.  -new-tab URL Open URL in a new tab in an already running Firefox process.

       -jsconsole
              Start with Javascript Console

       -chrome url
              Load the specified chrome.

       -safe-mode
              Starts Firefox in safe mode, that is disabling all extensions and showing a bit more debugging messages.

   Debugger options
       -g, -debug
              Starts Firefox through a debugger (gdb by default).

       --debugger program
              Use program as a debugger for Firefox. Implies -debug.

http://www.mozilla.org/docs/command-line-args.html
http://kb.mozillazine.org/Command_line_arguments

возможно ли командой скачать фаил например http://dfg.ru/12.rar, без диалога "сохранить"?

Firefox это вообще-то браузер, а не менеджер закачек.

wget юзайте - вот вам и скачка файлом и ключи и консоль в подаром.