Facebooker currently assumes ownership of your asset host. This is a problem for projects using a separate asset host.
Instead, only set it if it is not yet set.

--- a/vendor/plugins/facebooker/init.rb
+++ b/vendor/plugins/facebooker/init.rb
@@ -48,5 +48,5 @@ if File.exist?(facebook_config)
   ENV['FACEBOOK_API_KEY'] = FACEBOOKER['api_key']
   ENV['FACEBOOK_SECRET_KEY'] = FACEBOOKER['secret_key']
   ENV['FACEBOOKER_RELATIVE_URL_ROOT'] = FACEBOOKER['canvas_page_name']
-  ActionController::Base.asset_host = FACEBOOKER['callback_url']
+  ActionController::Base.asset_host ||= FACEBOOKER['callback_url']
 end