When viewing my website acro.batcave.net on different browsers like IE (Windows 7, IE 11.x) and FF (Windows 7, FF 37.x), I noticed that it appears differently. Chrome seems to have the same display as FF. The CSS file can be found at acro.batcave.net/css/index.css. Initially, I thought the issue might be due to non-standard CSS, with the intention of using CSS3 elements. However, after running the CSS validator on W3C, no errors were found. What could be causing this discrepancy and how can I ensure that FF (and Chrome) display it similarly to IE?