Our application is sometimes used in environments with no internet connectivity. And using the browser cache as the map tile source is quite acceptable in our scenario.
If Cesium first loads when online, we have no problem using it offline afterwards. The browser cache loads beautifully. However, if we try to start the application (and therefore Cesium) while offline, no map tiles are loaded.
Sorry for lacking details, but I have very little really. We are using an embedded CefSharp browser in C# based .NET application. And Chromium throws the following warning:
[0810/185229:WARNING:dns_config_service_win.cc(654)] Failed to read DnsConfig.
I can repeat the same scenario in a stand alone Firefox browser as well.