is there any way for someone to see what websites you were on at the same time as theirs?

let's say, hypothetically speaking, that you were reading fanfic in one tab while emailing a prof and looking at a friend's tumblr in others. could the prof see any of that? could the tumblr friend see that?

idrc if my friend on tumblr sees me reading fanfic or that i was emailing a prof, but if the prof saw the tumblr and fic, the friend would be outed to him and well idt my profs need to know all my feels about loki

yes ik i am paranoid and bad at using computers