The concern I have here is more about application transiency. Measuring `moz-app-loaded` is not really about indicating when the user has everything loaded to it, but more about measuring when the application should be in a stable state as far as rendering and loading of external resources that are not required for immediate user action. If it takes 3 seconds of inactivity to load the rest of these resources, then this is something that we will need to measure to consider the app to be completely loaded. When we are doing perf measurement for loading, we won't have any user interactions that delay this from loading any further.