Type about:customizing<enter> in the address bar. Look for Show / Hide Toolbars at the bottom left.

There is also a Restore Defaults button at the bottom middle.

Fred McD:

 Thank you very much for quickly solving this pesky problem.

 Vumbo

Note that you can use one of these to set which toolbars to show.

• "3-bar" menu button > Customize > Show/Hide Toolbars
• View > Toolbars
  You can tap the Alt key or press F10 to show the Menu Bar
• Right-click empty toolbar area

Glad to help. Safe Surfing.

The solution of using the 3 bar menu and customizing does not work. Must be something in the latest update that messes with everything. I suppose I did something to make the File-etc top line disappear but I can't think what. Maybe I should look for help with THAT and then work backwards. Installing updates should not be a mistake as often as it is. Thanks.

Make sure that you do not run Firefox in Full Screen mode (press F11 or Fn + F11 to toggle; Mac: Command+Shift+F).

• https://support.mozilla.org/kb/how-to-use-full-screen

When you are in Full Screen mode, hover the mouse to the top of the screen to make the Navigation Toolbar and Tab bar appear. You can use one of these to leave Full Screen mode:

• press the F11 key
• click the Maximize button at the right end of the Tab bar
• click the Full Screen button in the 3-bar Menu button drop-down list
• right-click empty space on a toolbar and click "Exit Full Screen Mode"

Try to rename (or delete) the xulstore.json file in the Firefox profile folder. You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox