I am not sure. Is this what you are looking for? browser.tabs.closeWindowWithLastTab

FredMcD, Many thanks for your quick response! For over 2 years I've had the pleasure of having what I call a "fixed" first tab in my Firefox. It simply was the result of seeing a message about how to turn that initial first tab into an anchor . When I opened Firefox and entered either a new address in the field or had a Bookmark do it and then was taken to said link the first tab passed it on to a "newly-called-on" tab or in some cases (took on that link itself) would immediately recreate itself before (as is the standard Firefox procedure/instruction) rather than closing Firefox. Again. many thanks..... Mark

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily.

Thank you for contacting Mozilla Support.

I assume you previously had a Legacy extension (Tab Mix Plus?) that replaced the last closed tab with the home page and prevented Firefox from closing. Firefox doesn't and didn't come with such a feature.

Hello cor-el, By "fixed Tab" I mean that no matter what the first Tab Always remains whether it was used to open your first desired connection and that connection is closed by you or not. While this means you must close Firefox when you are finished with said session using the title Bar's "X" or Menu's File/Exit. I have often found this to be very nice! I did fail to to save the formula for editing Firefox to feature this and would truly like to see it back in the reload of my favorite browser <G>!!! Many thanks.... Mark

See if this helps you; https://support.mozilla.org/en-US/kb/how-to-set-the-home-page