Correction: The Menu bar is up and running at all times. The top bar with the exit icon is not there on startup and needs the F11 button to be pressed once to go to full screen and include the exit icon bar then pressed again to allow the Windows bottom taskbar to be seen when not in full screen mode. Again, everything works will in partial screen exit and startup. It is missing when exiting full screen (with my Windows bottom taskbar showing) and needs the F11 key pressed twice to correct the problem.

You can try to manually enable and then disable the Menu Bar using the right-click context menu within Firefox.

Start Firefox

Press F11 twice to restore the screen, so you can see your usual bars.

Right-click on the blank area of the Tab Bar (next to the "+" sign for a new tab).

In the context menu, you should see an option for Menu Bar. Make sure it is checked (enabled).

Right-click again on the Tab Bar.

This time, uncheck the Menu Bar option to hide it again.

Now, close Firefox while it is not in Full Screen Mode.

Restart Firefox.

This action forces Firefox to re-save its window state configuration, and maybe resolving the issue.

Unfortunately, after implementing your workaround there was no change. When starting up in full screen the top bar with the X icon is missing. The menu bar is functioning properly in all screen configurations; either active or not. What I need fixed is the missing top bar with X icon always being available in full screen startup without having to press F11 twice. I don't want to press any key to have it properly appear (as it has for decades). It does appear normally when starting up and closing down in less than full screen.

Hello

Apparently a similar discussion.

https://connect.mozilla.org/t5/discussions/where-have-the-top-right-icons-gone/td-p/110549