FireFox – open only one tab please

Question – I have FireFox setup that when I launch it, it open 4 tabs and opens 4 different sites. If I open up a new window it always opens up these 4 tabs.

Is there a way to have a new window up with only one tab? Occasionally I like to open up a new instance of FF to keep certain tasks separate. I can always close my unwanted tabs but…

:ar!