To block loading of an "about:*" page, you just have to define a new boolean preference "[email protected]*" with the value "false". For example if you want to block loading of "about:permissions", just set "[email protected]ons" to "false". Otherwise - with no value or "true", the page is never blocked.
There are similar addons for specific "about:*" pages. They disables related menu items and others for the page, so they are recommended for general cases.
* "about:addons" : Disable Addons https://addons.mozilla.org/addon/disable-addons/
* "about:accounts" and "about:sync-*" : Disable Sync https://addons.mozilla.org/addon/disable-sync/
* "about:config" : Disable about:config https://addons.mozilla.org/addon/disable-aboutconfig/
This addon is created mainly for enterprise users.