Love to see that Virgin UK/O2 have blacklisted "http://detectportal.firefox.com/canonical.html" (the URL Ffox uses to invoke a captive portal, such as the ones you have to clear in order to use public hotspots with Virgin as a provider). Also nice to see that they've copyrighted the error page.
@pluralistic Oh no. It's that dangerous category "Computers and Technology".
anecdote: When I worked at Sony Ericsson/Mobile back in the early 2000s we launched the Walkman and Cybershot phones specialized in music and photography respectively. At the same time the IT-department blocked the category "media" for the whole company.
Lots of testing happened at home.

