For some reason, all of a sudden, when I try to do a Command-C, DEVONthink starts up and offers me a clip-to-DEVONthink. Command-C is now unavailable to me for normal use and I see no way to change key-mapping for clip-to-DEVONthink.
Never mind. I shoulda search the forum before posting. I see that the command sequence can be changed in Safari > Preferences > Extensions.
My apologies.