i've updated to the latest available xscreensaver using a PPA so i would get proper screensaver inhibition when using firefox and now the "disable screen saver" option no longer works when manually trying to disable it for fullscreen apps which don't inhibit xscreensaver...
because, no, setting "disable screen saver" does not turn off locking and the checkbox for disabling locking gets disabled when you turn to that mode, which according to https://www.jwz.org/xscreensaver/man2.html should not blank the screen and yet it does
using xscreensaver 6.02 on ubuntu-mate 20.04 "disable screen saver" mode does the same as "blank screen only"