Blog has issues in Firefox

Hmmm… so I thought I’d ‘browse happy’ and try switching over to Firefox, only to find out that in Firefox my sidebar has dropped to below my blog.
Can anybody help me combat this?

Thanks

https://www.engberts-kaya.com

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Edit: Actually, now a worse problem. In my ‘tinkering’, I deleted a bit about intro.php from my index.php to try to solve another problem, and now have a bigger problem. (See https://www.engberts-kaya.com). Even though I undid the changes and reuploaded the index.php, the problem remains.

The error message is: Fatal error: Call to undefined function get_header() in /home/engbeng3/public_html/index.php on line 1

The beginning of the code is:

<?php get_header(); ?>
	<div id="content">
		<?php include_once(TEMPLATEPATH.'/intro.php');?>
		<!-- Primary content: Stuff that goes in the primary content column (by default, the left column) -->
		<div id="primarycontainer">
			<div id="primarycontent">

Any idea what the error is?
And thanks Whooami for the advice on my other problem!