Further to my posting of yesterday, I hae found that by pressing F11 twice - i.e. toggling full-screen off and on - Firefox gets its top bar buttons. This gives a workaround and hopefully provides a clue as to the nature of the cause.
Further to my posting of yesterday, I hae found that by pressing F11 twice - i.e. toggling full-screen off and on - Firefox gets its top bar buttons. This gives a workaround and hopefully provides a clue as to the nature of the cause.