I know that was just one example, but I think you can view message headers in OWA by clicking the ellipsis on a message, then "View" > "View message details".

I know that was just one example, but I think you can view message headers in OWA by clicking the ellipsis on a message, then "View" > "View message details". Also, my mom preferred Safari but kept Chrome around for installing and opening PWAs. I understand if there's a philosophical reason this won't work for you though :)