Use Multiple Firefox Profiles at the Same Time

This is help full in many ways. I do use this in selenium automation to run multiple test case at the same time.
If we different user cert (authentication) for different step us, if i need to check one bug on another old set up which have different user cert installed i can just start that profile and test at the same time.

Step 1: Make Sure you have created Multiple Firefox Profile. If not see the sub steps how to create multiple profile.
        Step A: Open command prompt or Press Windows + R button
        Step B: On command prompt go to C:\Program Files\Mozilla Firefox location and Run below command
                    firefox.exe -P or firefox.exe -ProfileManager
                    If using Windows + R button then type same  command in Run
                    firefox.exe -P or firefox.exe -ProfileManager  
        Step C:  Click on Create Profile
        Step D:  Click on Next and Give the Profile Name
        Step E:   Now Click on Finish... Your newly created firefox profile is ready

Step2: Open command prompt or Press Windows + R button

Step 3: If command prompt then go to C:\Program Files\Mozilla Firefox location and type below command
            firefox.exe -P -no-remote  or   firefox.exe -ProfileManager -no-remote
            If pressing Windows + R then type the same above mention command in Run
            firefox.exe -P -no-remote  or   firefox.exe -ProfileManager -no-remote

NOTE : Make sure there is no space between -no and -remote

Step 4: Now select any profile which you want to run and press  "Start Firefox" button.
            or directly type firefox.exe -P -no-remote "ProfileName"
            You have started first profile successfully now try opening another profile at the same time.

Step 5: Follow Step3 again and run the same command again

Step 6: This time select another profile and press "Start Firefox". Your are running two different profile at a time.

You can check if you are opening two different profile or not by setting up Tools -> Option -> General -> and set two different home page for two different profile.Now start you two different profile at the same time and see if both profile are opening correct home page or not.

Of course there are other way to check the open profile name.
Explore more command/option for firefox profile manager
http://kb.mozillazine.org/Command_line_arguments

Hope this post will help you.