The wed-based mail reading method sometimes can provide tools we don't have in a dedicated email app! Are there any options for exporting that display or message from FF? I'm assuming you've already tried reading the message in Mail, or is that where it shows up as a file (icon) attachment? Even there, you might try right (control) clicking the attachment icon and see if you get something like a 'view as...' menu option. Mail tends to show multi-page documents as icons... or maybe that's just when creating a message!
Have you tried 'Printing' it as a PDF?
I just noticed, using
Chrome, that it wants to use its own Print Dialog instead of the one in the OS. It sounds like your dialog is the 'standard' one the OS uses, however. If not, there should be an option to use the 'standard' dialog which has the "PDF" button in the lower, left-hand part of the window.
Using the 'landscape' mode might also help.
Or simply using Copy & Paste? Copy the data/text in the email display and Paste it into a word/text processor?