Prefswitch allows you to add preference switches to the status-bar of your browser. To add your own preference rules (switches) you should know how to use Mozilla preferences. When ready you can go ahead and start creating `short-cuts' for configuring your Firefox.
Many preferences can be changed by one click (sometimes two). This allows something like changing proxy configurations or switching between a bunch of security settings.
You can manage profiles and the way preferences are configured when choosing a profile.
Take a look around.
 About:config entries - http://kb.mozillazine.org/About:config_entries