It's a bigger problem for Chrome. Imagine if you ran an ad on a major ad network that loaded a banner from your server that sent a byte as TCP urgent. It would lock up any Mac who visited a significant fraction of the Internet.
(Incidentally, a bug like this was what got me to switch from Netscape to Internet Explorer back in 2000. Doubleclick ran an ad that included some Javascript which locked up Netscape and hung the browser entirely, blocking roughly 40% of the Internet for me. At that point I was like "This is ridiculous, fix your damn software Netscape" and switched.)
(Incidentally, a bug like this was what got me to switch from Netscape to Internet Explorer back in 2000. Doubleclick ran an ad that included some Javascript which locked up Netscape and hung the browser entirely, blocking roughly 40% of the Internet for me. At that point I was like "This is ridiculous, fix your damn software Netscape" and switched.)