Can you otherwise enter Full Screen mode like via the View menu?

• View -> Full Screen
• you can tap the Alt key or press the F10 key to show the hidden Menu Bar temporarily

Note that it is possible that auto-hide toolbars is disabled.

• https://support.mozilla.org/en-US/kb/how-make-firefox-and-websites-go-full-screen

F11 used to toggle Full Screen ON/OFF—very useful!  Thanks for reply.  View Full Screen only enters Full Screen with no return, except Close and start anew with same URL typed. The application menu button still toggles Full Screen using zoom, but is inconvenient. This loss of Full Screen F11 toggle may be linked with Win 10 Pro update.  It occurs on both my Firefox and Edge browsers!  (I rarely use Edge.) My F11 key works physically (tested with keyboard checker!). Any thoughts?