Firefox by default handles all tabs the same way. A tab gets closed if a user presses the close button, no matter if that action was intended or not. It is also true that new websites get loaded in the active tab under certain circumstances which is another thing that some users might want to [...]
Firefox: Keep tabs permanently open
We all have some sites that we visit regularly throughout the day. It’s my site of course for me, Gmail and a forum that I hang out all the time. It does happen from time to time that I accidentally close one of those tabs that I need throughout the day only to find myself opening it again in the next second.

