If the whole classic menu bar is missing, you can display it temporarily by tapping the Alt key or pressing F10.

To keep it displayed, you can use one of these methods to show the toolbar list and select it there:

• right-click a blank spot on the tab bar (or the "+" button)
• tap the Alt key to activate the classic menu bar > View > Toolbars
• in Customize mode > Show/Hide Toolbars

Does that work? Is Email Link still there on the File menu?

By the way, some users lose their toolbar visibility settings by using the Refresh feature. This could happen if you see a message that Firefox is starting slowly and you could speed it up by restoring some default settings. If you use the button, an Old Firefox Data folder appears on your desktop containing your old settings folder. Do you see anything like that? I suggest hanging onto the folder for a few weeks in case you notice any critical data or add-ons missing.

You can try to open a new window via Ctrl+N in case you are in a pop-up window with toolbars hidden.

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

Try to rename (or delete) the xulstore.json and the sessionstore.js file in the Firefox profile folder.

You can use this button to go to the currently used Firefox profile folder:

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