Firefox / IE layout problem

Hello.
To make this quick, view the following page in IE then FF...

http://www.phpbbdesigns.com/login.php?style=44

In IE the two images that make up the left and right borders resize to fit the text. Whereas in FireFox the image is displayed at full length and doesn't resize.



(As the image is a squiggle rather than a straight line, setting it as the background doesn't work because the repeats don't quite line up....)

Any solution to get this to work with FireFox?

Thanks.