In the Firefox settings there is an option to show the “windows and tabs from last time” when starting up the browser. This is handy for anyone who wants to close their browser, but retain any windows and tabs that were previously open for the next session.
Previously I never understood how this feature could be used to restore windows without the help of an extension. When I close Firefox I always use the red “X” in the upper-right corner of the window. Doing that, as expected, would only make Firefox remember the last window that I had open.
In a comment on a previous post DKong and netster007x were able to make an intelligent observation that never even crossed my mind. If you use the File -> Exit command when closing Firefox all of the open Firefox windows will be closed at the same time. The next time you go to restart Firefox all of your previously opened windows will be restored.
I never really thought that there was a purpose to the File -> Exit command, and I figured it was just there because that’s standard practice. As it turns out there is a surprisingly useful reason for it to exist! The next time you want Firefox to remember your windows and your tabs just use File -> Exit.