Probably not enough RAM. The page isn't doing anything crazy, but includes a dozen or so example <video>'s, which in turn can send Linux into an out-of-memory situation that freezes the system (technically it's still working just really slow). Ran into that issue a lot when browsing around with 8GB RAM, upgrading that helped. Installing earlyoom[1] is another workaround.

[1] https://github.com/rfjakob/earlyoom