Firefox opened up a Evince instance for viewing a PDF document, Evince couldn't save in /var/www/anything either. Seems the permissions problem propagates to applications launched by Firefox.
I saved a copy of the PDF in my Desktop, then later I moved it to /var/www/anything, I opened it up from there with Evince and saved a copy in the same folder without problems. So I think it confirms it's because Firefox launched Evince with it's own restrictions.
Firefox opened up a Evince instance for viewing a PDF document, Evince couldn't save in /var/www/anything either. Seems the permissions problem propagates to applications launched by Firefox.
I saved a copy of the PDF in my Desktop, then later I moved it to /var/www/anything, I opened it up from there with Evince and saved a copy in the same folder without problems. So I think it confirms it's because Firefox launched Evince with it's own restrictions.