Use the Firefox Profile Manager to create multiple profiles.
- Windows Key + R to open the Run dialog, type firefox.exe -p and press Enter.
- Create your additional profile(s).
- Create additional shortcuts to these profiles by appending '-p ProfileName' to the shortcut Target: path in the shortcut properties.
Synced profiles can be logged out of by choosing Options, Sync, and the Disconnect button on your Firefox Account. You may need to clear synced data from the profile after disconnecting your account.
More information on setting up Firefox Profiles is at MakeUseOF and HowToGeek.