You don't need any special configuration to open multiple tabs to different videos and play the videos simultaneously. (You might need some ibuprofen after a while...) That doesn't work on yours?

is there a about:config or add-on that gives a mute/unmute for each individual tab located inside the tab header of each tab like a speaker button mute or unmute for individual tabs?

In the Firefox 89 redesign, the old speaker icon/mute button design changed:

• Normal tab density: the word PLAYING appears under the title on the tab and the speaker button appear when you mouse over the tab
• Compact tab density: the speaker button appears in place of the YouTube icon on the tab

Add-ons can't change that, and there's no about:config setting. (There is an unofficial/unsupported style hack for userChrome.css users if you are adventurous.)

When i change tabs the previous foreground(now background) tab that is playing stops playing when i start playing a new foreground tab. i would like to play both because i use the background for music, i watch international videos in other languages with auto translate in the foreground and often have a second split screen window on websites about the place or culture that is the video, i used to be able to do this on my previous laptop. so i am assuming it is a true/false cmd in about:config in media playback string but i am not savvy enough to know which.