Maybe I’m just getting old, but I am still a heavy keyboard user. So sometimes I am cleaning up my Firefox sessions using Ctrl-W to close windows and I get a little itchy and close that last tab and boom – Firefox closes. Ok, it is a little thing, but still annoying. But there is a solution using our good friend about:config. Just set the following to false, which is not the default.
If you are not familiar with about:config, just enter that in the address bar. Promise to be careful, then in the Filter box enter the first part of the string above, say browser.tabs and you should see that preference listed. Double-click it to change the value, at which point it will go bold indicating it is no longer at the default setting. You’re done.