@pp4mnklinux :-
Um.....basically, you can't. (And you're not the first to ask this, not by a LONG chalk).
As with any browser, you can create multiple profiles. However, from my own experience, you cannot run more than one at a time.....not if they're going to be working from the same browser installation.
I've never really understood why, but 'zilla-based browsers seem more susceptible to this than the Chromium 'clones'. Firefox does NOT like having multiple versions of itself open at the same time.....even when those versions are self-contained, as is the case with the 'portable' builds.
The only way I've ever found that you can run a different browser on each desktop is to open multiple 'portable' browsers, one per workspace. It's perfectly possible to open multiple versions of the same browser with the 'clones'; being self-contained, they won't interfere with each other. The Chromium code-base has always permitted opening a second, dedicated 'window' at the same time as an existing session of the browser anyway. I've never been able to duplicate this with Firefox, but then it's not my main browser.....so I don't spend anywhere near as much time investigating what it can & can't do.
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However, I will just add this. The above scenario is perfectly 'do-able' with plenty of resources.....my 32 GB lets me do all sorts of stuff that someone with only a few GB wouldn't be able to. It's not a practical solution for everyone, because those individual browsers each occupy a fair chunk of RAM. When you don't have much to play with, you do of course have to watch what you're doing with it.
Mike. 