Where to report Gitbook error (Problem loading page)
If you experience this problem when trying to view the documentation it may be that your browser is either Chrome or Firefox and that you have previously visited the same page prior to 22 March 2016 (or for Firefox perhaps just visiting the main site https://civicrm.org could be enough).

The gitbook link now redirects to http://docs.civicrm.org/user/en/4.6 (the read the docs version). The read the docs version previously used https and the switch to http can cause problems. I am not an expert on this but I know it has something to do with HSTS. I think that Chrome and Firefox will redirect to https even if you specifically enter http if the sub-domain previously used https. 

I was able to solve the problem with Chrome by deleting docs.civicrm.org from chrome://net-internals/#hsts (clearing caches or browser history did not work for me).

I have not yet managed to solve the problem with Firefox. Again clearing caches or browser history did not work for me.