How to make the images of a gallery page showing its set image size?

Link: http://sokastudio.com/#portfolio

Reproducing the problem:

1) Click on any project links on the left side bar with FireFox. (Works on other browsers tho.)
2) Refresh the page and click on the project links again (it takes a few times sometimes and the order of this bug is kinda random) and eventually you should see something like this: http://screencast.com/t/nAFTbOvNEIZs

I don't want the images to show up as 24x24 pixels thumbnails on Firefox.

Thank you!