Iframe overflow takes a new line instead of a scroll bar

I created a web site that shows the directory list in the server. In backend all the directories are getting indexed and shown in an another webpage called dirpage. So I used an iframe in mainpage to show the content of dirpage. The mainpage and dirpage are working great. But when the dirpage is shown in the iframe, the content overflows. The iframe width is limited to the <div> width. The problem is the iframe overflow is taking a new line to show the content.
Here is the main page.