Your web browser essentially works as a translator. It grabs a document written in HTML and translates it into a formatted web page. The solution is similar to providing two individuals with a sentence written in greek and asking them to communicate it to us in English. While the end result may be similar, the method used to achieve that result may be different. Both may have communicated the same meaning, but perphaps used alternate vocabulary to do so. The same can be said for a web document. No browser fully supports 100% of the HTML 5 standard, but some might come closer than others.
Your website may not appear the same across all browsers. Different browsers utilize various algorithms to display websites. This is why your website may seem very similar on Mozilla Firefox, Chrome and Safari, but may appear chaotic on internet explorer - especially versions lower than IE-9. Unfortunately, there is only so much that can be done to remedy this discrepency. We perform cross browser compatibility tests across certain browsers such as Firefox, Chrome, Opera, higher versions of IE and Safari to verify that your site is fully functional and structurally sound, although you can expect to witness minor structural variations between each platform.