So far, FF v89 seems to have fixed my issue with settings restore as closed topic so for now, a happy bunny!
I'm using it with MATE 21.04
EDIT: but then again... I tried later and no change 
Further Edit: It is working... somehow it seems to want to open in workspace 2 and it is persisting. Open another instance in workspace 1 and it defaults to the incorrect sizing/placement but w/s 2 instance persists after reboot. Interesting!