The list is at https://hg.mozilla.org/releases/mozilla-release/file/tip/toolkit/components/telemetry/Histograms.json https://hg.mozilla.org/releases/mozilla-rel

The list is at https://hg.mozilla.org/releases/mozilla-release/file/tip/toolkit/components/telemetry/Histograms.json https://hg.mozilla.org/releases/mozilla-release/file/tip/too... looking at the blame view will usually lead to the bug that introduced the probe. Short of the file being refactored, which case you need to look at the file before the refactoring happened. That will describe the reason and the data review that occurred before adding the probe. There is also the probe dictionary at https://telemetry.mozilla.org/probe-dictionary/?optout=true&channel=release https://telemetry.mozilla.org/probe-dictionary/?optout=true&... which is a bit easier to read.