This is a normal response on the browser. When closing out your only tab there is no other tabs to keep Mozilla Firefox open. Just any way to close out the browser.

When I open any other application, it just opens. I can open and close a file and the application only closes when I press alt-F4 or ctrl-q. Firefox should behave the same and it used to before. Please fix this. Thank you.

Enter about:config in the URL bar and set browser.tabs.closeWindowWithLastTab = false.

Thanks!