For the browser version, try playing on a different browser like Chrome or Firefox. Make sure you are close to your wi-fi source. :)
For the download version, I tried and couldn't replicate the bug with my Mac. May be a gtx issue. Is your graphics card driver up to date?
I am already playing from chrome, it still doesn't work :(
I don't know about my graphics card – as far as I can tell it's called something like "Intel HD Graphics 6000 1536 MB", but I have to admit I don't really know what that means haha....