Its the way the link has been generated from the home page. It specifies to open in a popup window as opposed to a full browser
href="javascript
penpopup_27b5('http://www.gasgasrider.org/forum/index.php')"
I just navigate to
www.gasgasrider.org/forum to get a page with all the buttons
As others have said. Add it to your favourites!