Portfolio page (and oddness with images)

My portfolio project page is here: https://acavender.github.io/portfolio-fcc/.

I’m generally pleased with how it turned out, but I’m a bit puzzled by one thing. The images in the portfolio section render fine in Safari, Opera, and Chrome. But in Firefox and Edge, they display very small for some reason.

If anyone has any ideas about why that is, they’d be appreciated!