When viewing my site in Google Chrome, the thumbnails look correct, and the portfolio page looks perfect, however, when viewing in Firefox or Internet Explorer, the images are full size and overlapping.
The link you provide works nice on firefox, chrome and internet explorer on our computers please have a look at your end by refreshing the cache, if still the problem arises could you please share us a screenshot.
Sorry for misunderstanding, i thought you were taking about the portfolio on the home page. and regarding the problem you can use the following custom CSS to fix the problem.