Adding Firefox profiles is pretty straightforward, as is using them. To open Firefox’ profilemanager, you first make sure Firefox is completely shut down, then you open a terminal (or type ALT+F2 to bring up the application launcher):

firefox -profilemanager

A window will appear with all the existing profiles as well as options to create/edit/delete profiles. Use of the manager is straightforward and should not require an explanation. To use profiles, enter

firefox -P "Profile name"

Note that you can also use this command in the “Create Launcher” window to make an application shortcut using that profile. More information on profiles can be found at Mozillazine.