Builds are done locally on your machine and pushed to production with the firebase deploy command. The example application uses npm to build the site using webpack.
Functions that can be triggered on a database update, http request or some other event. Caching is controlled via the Cache-Control header returned in the response. Routing to functions are controlled in firebase.json, static files are ALWAYS be served first. Local dev mode can be done using firebase serve --only functions.
Clients inject a script that collect information about page load times. This is similar to how Google Analytics works. The metrics are displayed as a distribution of load times up to P95, which very clearly shows the longtail of load times. More detailed metrics are collected from an API called NetInfo