Firefox does support multiple profiles (not containers but fully isolated profiles) even though it's not exposed in the GUI.
New profiles can be created from Profile Manager (-ProfileManager command line flag) or from about:profiles. A new windows can be started with a different profile either using -P <profile> command line option or from about:profiles.

@raindev or from the shell; use these options to force firefox to bring up a new instance, with the profile pop-up: firefox -no-remote -P &

@uuim that's useful too if you prefer launching windows with different profiles centrally (e.g. from a shortcut) rather than from an existing window. But `-P <profile>` skips one more step if launching from command line and profiles are set up already.

unsolicited advice 

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