For me it just caused Safari to stop working until I quit and restarted it.

On my M1 MacBook Air with MacOS 12 it hangs. The mouse pointer still moves, but I can't bring up the force quit dialogue, and couldn't get anything else to work either. A youtube video in another tab kept playing until I held the power button to force a shutdown.

I'm using macOS 27.0 RC on M4 Max

A Denial of Browsing attack.

I have two other web browsers open at any given time, so probably not really. I guess it would be if it truly did bring down the entire system.