Type about:config in the Location bar and hit Enter. Accept the warning.

browser.tabs.closeWindowWithLastTab

double-click to toggle to false and then restart Firefox.

Now if you close the last tab the window (or Firefox) won't close, but a New Tab will be there.

No. Put this option in the options screen. Too many hidden options in Firefox. Its so stupid, and you keep taking more that used to be visible out and hiding them in about:config. Its so annoying.

Hi developerwjk, this is the support site for the existing Firefox. To make feature suggestions for future versions, you can submit comments here:

https://input.mozilla.org/feedback