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Firefox is adding profiles to separate your browsing sessions
(www.theverge.com)
This is a most excellent place for technology news and articles.
Just add -P to Firefox launch flags once and then selected "prompt me everytime". This also has been true for rlike 20 years.
Or just -P "profilename" to launch that profile directly from a shortcut.
You can have as many running simultaneously as you'd want.
it's slightly different; before to have two profiles open at the same time you had to add no-remote and it was still quirky; now its much more streamlines and background links outside of firefox will open in whichever profile has focus.