Thanks! I've never actually played Skyblock myself but who knows, it might have subconsciously influenced me ;)
I only tested on firefox before and for me it opens fullscreen in a new window (don't know why). When I tested Chrome later I had the same issues you describe. I changed some settings and at least the resolution is now fixed on Chrome. Let me know if firefox still doesn't load. Not sure if I can fix that but then I at least know about it!