The closest I got was to start Firefox with a new profile, remove (most) buttons, and then create a shortcut not to the URL, but to the FF executable: C:\Program Files (x86)\Mozilla Firefox\firefox.exe" -no-remote -profile d:\temp\newprofile -height 400 -width 400 http://www.google.com
. See here for more options.
The address bar cannot be removed in this way, but it seems that you can do that by adding #nav-bar { display: none !important; }
to userChrome.css which should be in the chrome subfolder of the profile folder. If it's not there, create it manually and restart Firefox.
The -no-remote option makes sure that the specified profile will be used, even if Firefox is already running under another profile.