Ha!
I don't use much Javascript, so I didn't know the code off the top of my head, other than a simple window.open("www.website.com")
Go to this link and scroll down to the open method to get more details.
By the way, it would be better to just have the javascript hardcoded. I wrote my previous code thinking you had the javascript part already figured out.
It would be more like:
<form> <input type="button" value="open in browser" onclick = "window.open('<?php echo $MyURL?>',[other attributes...])></form>