On my desktop with a 23'' screen, I have multiple installations of Firefox portable, each for its own general purpose, and which load separately, though to enable then to run concurrently, in your profile folder you need place and edit a copy of the FirefoxPortable.ini from Other\Source to the main folder of FirefoxPortable (in Windows, not Linux, you can just right click on the shortcut Firefox icon, then hit Properties, then Open File location which is where you want to place FirefoxPortable.ini, which is to be found and copied from in the Other>Source folder. Paste and then edit/change that FirefoxPortable.ini to AllowMultipleInstances=true DisableIntelligentStart=true.
And in W/11 to enable separate taskbar icons I had to set “taskbar.grouping.useprofile” preference in about:config to true. I use 7+ Taskbar Tweaker and which author has been helpful, thanks be to God for such.
I also run two "stand-alone" installs of Chromium-based Vivaldi, and one of Gecko-based Floorp (from Japan).
Yes, I have a lot of RAM, praise God. May all we have be used for His purpose, and to His glory, not that I always have or do.
Your posts are always detailed, enlightening, and accurate. I very much appreciate your expertise and willingness to share.