I've just discovered that git:// urls are blocked by internal policy. Frustrating. Fortunately http:// and https://github.com/etc still work for git commands.
Frontend tools such as Bower they assume that git:// urls will be fine, which if they are not creates lots of error messages.
However you can set your git config to rewrite the default protocol with the following command in the terminal:
git config --global url.https://github.com/.insteadOf git://github.com/
Many thanks to Tobu on StackOverflow for pointing this one out.