When using via https://www.cl.cam.ac.uk/meters/tools/wgb-vis/current/index.html# in Chromium 18.0.1025.168 (Developer Build 134367 Linux) Ubuntu 12.04 I get the following red error message appear:
"Error HTTP error 0 when trying to access 'http://www.cl.cam.ac.uk/~cce25/indextest/config.json'"
Then the message goes away. I get the same issue in Firefox. It works over HTTP.
It would be nice if it didn't mind whether http or https was being used.