works as expect! love it.

one flaw (-1 star) the pinned tabs will be closed if the window is closed.
workaround (as per github source): instead of closing windows right click the further most right pinned tab and click "close tabs to the right". this way the pinned tabs will stay alive, move to a different firefox window when opened and the old "empty" window will close automatically

this is one of my favorite addons! works just like it says it does. i dont have to go digging around windows to answer the message that came in or accidentally open the message window again because i closed the window the pinned tab was in.

A recommendation:

https://github.com/Drive4ik/simple-tab-groups/issues/286#issuecomment-787110861