Yes! Either F10 or Alt will display the classic Menu Bar temporarily.

You can turn on (or turn off) Firefox's Menu Bar (and/or Bookmarks Toolbar) using one of these methods to show the toolbar list:

• 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?

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. Then 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.