Sites using the Persona polyfill begin recording KPI data on sign-in button click. Currently, on FirefoxOS, we only begin recording when the dialog is opened. We should modify the platform code to begin recording on button click.
In the shim, we do this by passing "start_time", a JS date, to the dialog from internalWatch. https://github.com/mozilla/browserid/blob/6a8b8efacfe8d46a04dc380c20dc0c1e22ee1d06/resources/static/include_js/_include.js#L355
Persona and Firefox OS have both been discontinued. Closing this as WONTFIX.