It isn't behind the Great Firewall, but it is behind an increasing number of government controlled boxes that could be turned into the Little Firewall. There are many direct fiber paths into HK that go directly to big companies and it would take time to bring them under control, but it would take only be a matter of time.

The other aspect of the Great Firewall is the alternative ecosystem inside it, and the censorship system embedded in weibo etc. It will be interesting to see if surveillance capitalism apps like Wepay and Alipay suffer a setback in HK in the wake of the protests. Cf https://www.bloomberg.com/news/articles/2018-05-24/alipay-s-...