Run multiple instances of the same version of Firefox with different profiles simultaneously
Your question is asking for something technically possible, in that it may be possble to "split" data in your profile, and distribute it among other profiles, but it sounds incredibly difficult to do considering what you would you gain doing this manually, as opposed to simply setting up new profiles and entering the data you wish into each new profile, and deleting the data from the other profile.

To accomplish everything you're asking for (except this splitting of the original profile data) is largely academic. The basic idea is have multiple profiles, and have multiple instances of Firefox each accessing a different profile. The way you do that is you first set up the multiple profiles, and you can do this by accessing the Profile Manager. Open your /Applications/Utilities/Terminal.app and type this at the command prompt:

 /Applications/Firefox.app/Contents/MacOS/firefox-bin -profilemanager &amp;


and the window that appears, along with information at the link provided above, will get you started on creating the extra profiles. Once these profiles are created, you can start the first instance of Firefox by clicking the Start Firefox button, and you can then launch your subsequent instances of Firefox using that same command. Again, in Terminal.app type the following:

 /Applications/Firefox.app/Contents/MacOS/firefox-bin -profilemanager &amp;


and you will see a second instance of Firefox appear in your dock. Choose the profile you wish for the second Firefox instance, and click Start Firefox. Repeat these steps (pressing the up arrow will display the last command) for as many instances of Firefox that you wish to run, or until you run out of memory.