Source Code Issue

Hey Guys, hopefully you can help me out with a problem I’ve been having.

I’m have just began working on a site and have come across the following issue;

The site itself is extremely basic. Containing only a home page, a media page and a contact page. I’m using a free them called Brominerary and including NextGen Gallery in the sidebar and also in the main container.There are also youtube embeds. The problem is that in some browsers (FF and IE) my footer and parts of the sidebar are being ‘cut off’ from the source code depending on what is on the page.

eg. At the moment there is a paginated ngen gallery and a Youtube video shown on the media page and everything is fine. But as soon as I add another youtube video embed, it’s as if the source gets pushed down the page and part of the sidebar and footer aren’t getting read anymore

I apologise if this makes little sense but I’d really appreciate some help with it.

Thanks