I replied incompletely to my forum post Feedback to Firefox team & WARNING to its users, and, though that solved my immediate problem, I'd like to augment it with this message, so as to describe a further problem....
Generally, if Firefox supports only a chosen (maybe I should say "proprietary"?) Firefox way of doing anything (like exiting via the menu only) on a major Firefox platform, like Windows -- and not all typical if not standard ways Windows users are accustomed to doing it -- there will surely be many unhappy Firefox users, and it's this kind of thing that can result in Windows users considering Firefox unfriendly or finicky, resulting in their preference for & use of another browser, like Edge or Chrome or Brave or whatever. In my opinion (trying to be helpful to the Firefox team & to Mozilla generally), the Firefox development team should be sensitive to the ways users are accustomed to working and take them into consideration, if it wants Firefox's user base to expand beyond its current boundaries.
In this case, it is my firm belief that the Firefox team should immediately change the Settings page in the first (General) section, to assert that users should use Firefox standards, which might be a subset of the standards to which they might be accustomed, to avoid issues like the one I had.
Secondly, I believe the Firefox team should work to cover those other standards that represent typical manners of use (ways of using Web-based applications) that the user base expects to be covered.
My intent is not to preach, but to emphasize the impact upon the size of the Firefox user base that things like this cause. I want the Firefox user base to expand to its fullest, and hindrances need to be removed to make this happen.
Thank you for reading. I know that developers may not appreciate all this, and I'll likely be hammered for it, but product managers & marketers will understand & appreciate it, I think, and this is being written by one who has worked from kernel system programming through consulting regarding technical as well as large-scale business excellence & success.
When a user closes a window, what factors should Firefox use to determine whether the user is finished with that window (and would be annoyed to see it restored) versus not finished with that window (and expects it to be restored)?