You copy/make a shortcut to Firefox. Then edit the target to: "C:\Program Files\Mozilla Firefox\firefox.exe" -P ProfileName -no-remote where ProfileName is the name you set during the (convoluted) setup.

-no-remote isn’t needed on the first profile you launch but is needed on subsequent profiles you want to run concurrent to the first one.

Edit: I have up to six profiles I run at once, and I also use the Container Tabs extension.