The feature exists on desktop, works great, but the setup is convoluted. https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles There’s a way to make desktop shortcuts to easily pick profile, but I don’t remember how, it has been a few years since I needed profiles.
Wish they had something for mobile too, that would be huge. I use my phone for both work and personal stuff all the time, not my desktop.
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.