Unable to minimize Firefox 91.5.0esr at top of frame

[John Boxall <jboxall47@gmail.com>]

After upgrading to the latest Debian 10 (Buster) Firefox ESR (91.5.0esr 
64bit), I found that I could not minimize the window by right clicking 
on the top of the window frame and selecting "Minimize", whether the 
menu bar was present or not. The menu for selecting minimize was not 
even present. I was able to perform the minimize with the old (78.x) 
release. I recently installed the latest FF release from the Mozilla 
site (version 95.0.2 64bit) and noted the same situation.

Is this expected going forward or is this a bug?
--
Regards,

John Boxall