Firefox on macOS loads, opening all windows open at last Quit; then closes all windows; fails to display the window selected from menu

<I chose Performance and connectivity only because the designers do not provide a choice that fits my problem, and do not provide 'Other' as a choice.> MacOS Sequoia 15.7.7; Firefox 141.0.2 The "one sentence" in the heading states the problem. I am unable to use Firefox. Firefox loads. It opens windows (I had fourteen open when I last used it successfully; I have many, many tabs). Then it removes each window from the screen. Firefox is in the Menu bar, but no windows are displayed. The windows still show when selecting Window in the menu bar. Selecting a window has no visible effect. File>New Window opens a new window, which works as expected. With one new window open, File>New Window does not open another. Typing a few characters in the Address Bar opens a dropdown with a list of tabs, each with the affordance, Switch to Tab. Clicking on one takes down the list but does not open a window. I would like, for a start, instructions on how to use Firefox starting afresh with no windows. First: having set aside the data that causes this problem. I suppose that might be simply a new profile.