You can use http://validator.w3.org to validate your page. It will give you the lines and columns where there is a problem. Once you fixed all the problems, you will have a very clean code and your web page should display consistently accros all platforms.
I had the same problem with my website, browsing on the internet I found the following code:
Your page has the following code:
You want to have "transitional" rather than "strict."
Here is the source where I found the code that helpd me, it has lots of good information: