The numbers are actually much better! The histogram is only reported once per browser session, at startup (it's scheduled [here](https://searchfox.org/mozilla-central/rev/f1e99da78fe6c3c68696358dac06aed90f8112d3/browser/components/BrowserGlue.jsm#2014)). We can receive multiple pings per browser session; browser sessions can span multiple calendar days. On all subsequent pings in a browser session, `histogram_parent_cookie_behavior` will be NULL. The query at https://sql.telemetry.mozilla.org/queries/65049/source#165711 treats NULL as "off". If the browser is used for multiple days, the user will be recorded as having ETP turned off for all days except the first. A new query at https://sql.telemetry.mozilla.org/queries/65059/source#165731 additionally aggregates by session_id, so that it only counts users on the day they sent their first ping from a browser session (i.e. the ping that contains the histogram value). It shows values much closer to 99% over the reporting period.
Bug 1584308 Comment 1 Edit History
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The numbers are actually much better! The histogram is only reported once per browser session, at startup (it's scheduled [here](https://searchfox.org/mozilla-central/rev/f1e99da78fe6c3c68696358dac06aed90f8112d3/browser/components/BrowserGlue.jsm#2014)). We can receive multiple pings per browser session; browser sessions can span multiple calendar days. On all subsequent pings in a browser session, `histogram_parent_cookie_behavior` will be NULL. The query at https://sql.telemetry.mozilla.org/queries/65049/source#165711 treats NULL as "off" and aggregates by UTC calendar days. If the browser is used for multiple days, the user will be recorded as having ETP turned off for all days except the first. A new query at https://sql.telemetry.mozilla.org/queries/65059/source#165731 additionally aggregates by session_id, so that it only counts users on the day they sent their first ping from a browser session (i.e. the ping that contains the histogram value). It shows values much closer to 99% over the reporting period.