I don't know why but
show Desktop Ctrl-Alt-D suddenly stopped working for Firefox only (in all workspaces).
Any ideas what might have caused this?
Thank you all!
ps: alt-space-n or ctrl-alt-arrow_key both continue to function normally (as a quick and effective work-around).
pps: in keyconfig I can't see any addon using this combination; plus, I did not install a new addon recently...