Problems standardizing my layout across browsers

I’m having trouble standardizing the display of of a list of products, primarily when my page is viewed on a ipad.
When viewed on an ipad in landscape or portrait view, I wouldn’t mind if there was only one item displayed on a line when viewed in portrait position but would prefer that there were two items when an ipad is held horizontally as is the case across ie, chrome, and ff.
Here is my page. http://www.duplex-pump.com/products/gaso

I’ve been stuck on this for several days but can’t seem to find the resources that would help me fix this.

I appreciate any help you can offer.