Images rendering differently depending on browser

This note came in via ZenDesk:

Hi,

I'm trying to implement the StoryMap on my Wordpress site using the
Wordpress plugin, but I'm seeming to run into some browser compatibility
issues. I'm not sure if some of it is attributable to the particular theme
that I'm using, or if there is something else going on.

I've attached a few screenshots of how things are currently rendering on my
in-development website. in Chrome, everything seems to appear correct.
Pictures are appropriately scaled and text is conforming to the container.
In Firefox, the text conforms to the container, but the pictures are quite
small. In IE, the photos are too large and the text is not conforming to
the container.

When I looked into this originally, the demo map on the frontpage of your
website at http://storymap.knightlab.com/ seemed to reproduce these
problems, but I have not since been able to get it to reproduce the IE
problem. The different scale of pictures in Firefox and Chrome is still
present though.

Any thoughts or suggestions you might have would be appreciated.

Thanks so much in advance,