Firefox definitely should not close windows on its own. Are you able to reopen them using one of the usual methods:

• Keyboard shortcut Ctrl+Shift+N
• menu button > History > Recently Closed Windows
• (menu bar) History > Recently Closed Windows

Firefox warns me when I use menu > Exit about all the open windows and tabs. Is this because I have Firefox set to restore my previous session at startup? You could double-check that you have this preference set:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future. Since we are confirming the default, I feel comfortable mentioning it.

(2) In the search box in the page, type or paste browser.warnOnQuit and pause while the list is filtered

(3) If the preference is bolded and "modified" to false, double-click it to restore the default value of true

Speaking of about:config, if you need Firefox to remember more closed windows for the Recently Closed Windows menu, you can adjust that value here:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future. Since we have had this setting for a long time and I use it myself, I feel comfortable mentioning it.

(2) In the search box in the page, type or paste browser.sessionstore.max_windows_undo and pause while the list is filtered

(3) Double-click the preference to display an editing field, and change the value to 10 (or whatever makes sense for your needs) then press Enter or click the blue check mark button to save the change.

Hi: Perhaps I should correct myself about the browser windows closed on their own. They are just not listed , not closed (as I was wondering why they are not listed in the history of recently closed windows) . When I pinned Firefox onto the taskbar in Windows 11, the windows were listed in a long list since I had many windows opened . The list provides a DOWN arrow for going down the list if the list gets too long but it does not provide or at least the UP arrow does not appear at the top of the list most of the time. I have to close some windows to make room in the list for other windows to be listed, so as soon as I have made room , those "disappeared" windows are listed and I am able to click on them) . The list will go to the top of the screen if it gets long . The UP arrow does not appear or is not seen since the list really gets to the top edge of the screen (I am already at the max resolution of the monitor) . I think the list should provide both UP and DOWN arrows to allow user scrolling the list when it gets to three quarter of the screen height. Also, I do not know if there is a setting for it, the list is sometimes replaced by a horizon list of thumbnail images of the browser windows, that arrangement is worse for me and I have no control when Firefox decides to switch to that list mode, or this is controlled by Windows 11? Thank you for the suggestion of browser.sessionstore.max_windows_undo , I was going to ask about that because the default of 3 is really limiting, so this helps .

The way the Taskbar works is most controlled by Windows, especially the question of when the thumbnails have reached the point of being so numerous that a list is displayed instead.

With my font size, it appears I can fit 32 windows on the Taskbar popup list before the scroll triangles appear. Your font size may vary.

It would be possible for a Firefox add-on to create a "Window" menu, but thinking about it, that would be shorter than what Windows shows now, so I guess it would need to split the window list into multiple columns to solve the problem.

In my own workflow, I tend to use Alt+Tab to switch windows (press once and keep holding Alt, then Tab as many times as needed and release when the desired window is selected). That's not optimal, either, if you need a window you haven't accessed for a while.

I too used the ALT-TAB combination to check for the windows currently running but I just couldn't find the windows that I thought were missing. I am reluctant to install more add-ons or extensions. I try to keep them to the minimum because every time you add or install something , it is like "contamination" to the system . A new system starts off fine and run smoothly at the beginning , after a while it becomes sluggish. I enjoy the "smoothness" with Win11 now much like I was with Vista from which I recently migrated , but after so many years , even though it is still running , it becomes sluggish ( for the browser , it is probably all the scripts and extensions) . As for font size , I already set it to the smallest one that my eyes can see , I don't want them too small as I need to sit closer to the monitor which I don't want to do. I wonder if Firefox has a developer tool that allows user to see what windows are running with their titles (names of the web sites).... Anyway, thanks for your help.