To run multiple Tor Browsers at once, see this
This method launches multiple Tor instances, each with its own SocksPort and ControlPort. This ensures that the Tor Browsers are fully functional, portable, and self-contained. However, someone should confirm that I haven't missed anything that could compromise TBs security.
- Optional: Download, verify, and install Tor Browser.
- Make copies of the Tor Browser folder with different names (eg. Number them)
- Launch Tor Browser
- Edit about:config
- Modify extensions.torlauncher.control_port to a new ControlPort (eg. 9052 for Tor Browser 2)
- Edit Torbutton Preferences
- Use custom proxy settings, and change the Port to SocksPort (eg. 9152 for Tor Browser 2)
- Close Tor Browser
- Edit torrc-defaults in \TorBrowser\Data\Tor
- Change SocksPort to what you set in step 5
- Change ControlPort to what you set in step 4
- Launch Tor Browser, and check that everything was configured correctly
- Homepage (about:tor) should say "Congratulations!"
- Click "Test Tor Network Settings". check.torproject.org should say "Congratulations."
- Go to ip-check.info. Test should be all green and orange except Tab name. Authentication should be "protected". Note: It may not say that you are using Tor, but this is incorrect.
- Optional: Go to ipleak.net for IP, DNS, Geolocation, Browser and other info
- Optional: Test your browser fingerprint at panopticlick.eff.org
- Optional: Edit about:config
- Type “banned" and modify the ports of the two entries. Add all the new SocksPort and ControlPort to the list (Copy the ports from other Tor Browsers)
- Optional: Turn on “Forbid Scripts Globally” in NoScript for further security and privacy (also reduces browser fingerprint)
- Repeat 3-10 for each Tor Browser folder
Alternatively, this might be possible with a single Tor instance as the SocksPort and ControlPort. This would require the use of the control_auth_cookie (CookieAuthentication) or HashedControlPassword, and about:config extensions.torlauncher.start_tor=false. However, the browsers would not be self-contained and portable, as they would require a process that isn’t in their own directory.
Inspired by mirimir's answer which seemed to compromise TB's security.