Firefox issue with twentytwelve theme

I was working on a site with wordpress 3.5.2 and everything was fine, but when I moved my site from one host to another I began to experience issues with the site working in Firefox. A splash screen is supposed to show up when the site is reached but it is simply a white page in firefox. When you click on the white page, it leads you to the site but the site does not look the same as it does in other browsers. I was told that there was an issue with the theme, but I did not want to update in fear of loosing my custom templates and stylesheets.