Yes, I know. The website doesn't load correctly in the In-Game Web Browser because the In-Game Web Browser is a pile of junk. Many in the Garry's Mod community have discussed the need for it to be updated/replaced, however
Garry doesn't want it to happen, for reasons unknown and much to our chagrin.
It also doesn't help that Hitbox's website has something like 4MB of JavaScript code, which drastically increases the chances of something breaking with such an out of date built-in browser.
We apologize for any inconvenience, however this isn't a bug we can fix. Please use a web browser outside of GMod, or even the one present in the Steam Overlay, instead.