Yes. Pinned tabs is doing this job but pinned tabs is doing some part of this but not the whole part it. Lets say, I have a video playing in a mini window and also bunch other tabs open. I have closed the tab that powers the video playing window soo many time while closing rest of the tabs. But not just that, lets say I have an important tab open, when I am quitting (macos command + q) firefox, I want to see a warning.