Opening a new instance of your Mozilla application with another profile
From MozillaZine Knowledge Base
This article explains how to open multiple instances of your Mozilla application at the same time, using different profiles. It was written for Firefox but also applies to Thunderbird and SeaMonkey 2. Thunderbird users should read Run multiple copies of Thunderbird at the same time for additional information.
Important: Never use -no-remote to start the "default" profile (the one that is set to open without asking when you launch Firefox). That's because when you launch Firefox, for example, by clicking a link in your mail program, you will get a Firefox is already running but is not responding message if the default profile is already in use. The solution is to always start the default profile normally and launch all others with -no-remote. Then it will work. 
You can use a shortcut to a specific profile to open Firefox using
"C:\Program Files\Mozilla Firefox\firefox.exe" -P "My Profile" -no-remote
Note: You can also open the Profile Manager with Firefox already running, by using
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