a ? about firefox

when I used 2 tabs and I was clicking on the X in the top right corner, they were asking me if I really wanted to close the window, because I had several tabs opened. I was clicking on no obviously, because I only wanted to close that page and not them all. But for some reason I dont have that warning anymore and it really bugs me, cause I always close all windows without paying attention :(

Anyone know how I can get it back? (>.<)

I'm not sure, maybe you used to have some sort of tab extension that added the feature?

Nos.

I'm not being very helpful, but in your address bar type: about:config

Browse through the list and see if there is a line mentioning a notification when closing the browser.