Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

14 files changed, 1258 insertions, 0 deletions

diff --git a/toolkit/components/glean/docs/dev/builtin_pings.md b/toolkit/components/glean/docs/dev/builtin_pings.md
new file mode 100644
index 0000000000..cbfff8c559
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/builtin_pings.md
@@ -0,0 +1,13 @@
+# Built-in Pings
+
+FOG embeds the Glean SDK so
+[its documentation on pings is authoritative](https://mozilla.github.io/glean/book/user/pings/index.html).
+The only detail FOG adds is to clarify
+[the "baseline" ping's schedule](https://mozilla.github.io/glean/book/user/pings/baseline.html#scheduling).
+Specifically, in Firefox Desktop, the application is considered
+* "active" when started,
+  or when a user interacts with Firefox after a 20min period of inactivity,
+* "inactive" after the user stops interacting with Firefox after 2min of activity.
+
+For more details about why, see the bug tree around
+[bug 1635242](https://bugzilla.mozilla.org/show_bug.cgi?id=1635242).
diff --git a/toolkit/components/glean/docs/dev/code_organization.md b/toolkit/components/glean/docs/dev/code_organization.md
new file mode 100644
index 0000000000..e943dbfd50
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/code_organization.md
@@ -0,0 +1,56 @@
+# FOG code organization
+
+![Modules of Project FOG](images/fog-modules.svg)
+
+The diagram shows the different modules of Project FOG.
+
+## FOG control
+
+This module is the glue between Firefox and Glean.
+
+* The code lives in `toolkit/components/glean/src`.
+* It is written in Rust.
+* The crate is named `fog_control`.
+* It is not published to crates.io.
+* It is not consumed by other Rust crates inside mozilla-central.
+
+This module is responsible for
+
+* collecting and assembling the [client information](https://mozilla.github.io/glean/book/user/pings/index.html#the-client_info-section)
+* configuring the Glean SDK via the Rust Language Binding
+* watching the Firefox Telemetry data upload preference (`datareporting.healthreport.uploadEnabled`)
+* scheduling builtin pings
+* controling ping upload workers
+* passing IPC buffers
+
+It calls into `glean` (the Glean SDK Rust Language Binding) to:
+
+* configure and initialize Glean
+* toggle `upload_enabled`
+* get upload tasks
+
+It calls into `fog` to:
+
+* pass IPC buffers
+* record to its own metrics
+
+## FOG API
+
+This module provides the user-facing API for Glean inside mozilla-central.
+
+* The code lives in `toolkit/components/glean/api`.
+* It is written in Rust.
+* The crate is named `fog`.
+* It is not published to crates.io.
+* It can be consumed by other Rust crates inside mozilla-central for their Glean usage.
+
+This module is responsible for
+
+* exposing a specific metric API in Rust
+* wrapping metric implementations for handling IPC
+* exposing FFI functionality to implement other language APIs on top.
+  See also [Adding a New Metric Type](new_metric_types.md).
+
+It calls into `glean` (the Glean SDK Rust Language Binding) for:
+
+* metric types (including pings)
diff --git a/toolkit/components/glean/docs/dev/images/fog-modules.svg b/toolkit/components/glean/docs/dev/images/fog-modules.svg
new file mode 100644
index 0000000000..c0271e9f6e
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/images/fog-modules.svg
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
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height: 1px; padding-top: 10px; margin-left: 481px;"><div style="box-sizing: border-box; font-size: 0; text-align: center; "><div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; ">Rust</div></div></div></foreignObject><text x="540" y="14" fill="#000000" font-family="Helvetica" font-size="12px" text-anchor="middle">Rust</text></switch></g><rect x="480" y="30" width="120" height="20" fill="#f8cecc" stroke="#b85450" pointer-events="all"/><g transform="translate(-0.5 -0.5)"><switch><foreignObject style="overflow: visible; text-align: left;" pointer-events="none" width="100%" height="100%" requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"><div xmlns="http://www.w3.org/1999/xhtml" style="display: flex; align-items: unsafe center; justify-content: unsafe center; width: 118px; height: 1px; padding-top: 40px; margin-left: 481px;"><div style="box-sizing: border-box; font-size: 0; text-align: center; "><div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; ">C++</div></div></div></foreignObject><text x="540" y="44" fill="#000000" font-family="Helvetica" font-size="12px" text-anchor="middle">C++</text></switch></g><path d="M 230 220 L 270 260 L 230 300 L 190 260 Z" fill="#ffffff" stroke="#000000" stroke-miterlimit="10" pointer-events="all"/><g transform="translate(-0.5 -0.5)"><switch><foreignObject style="overflow: visible; text-align: left;" pointer-events="none" width="100%" height="100%" requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"><div xmlns="http://www.w3.org/1999/xhtml" style="display: flex; align-items: unsafe center; justify-content: unsafe center; width: 78px; height: 1px; padding-top: 260px; margin-left: 191px;"><div style="box-sizing: border-box; font-size: 0; text-align: center; "><div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; ">IPC parent?</div></div></div></foreignObject><text x="230" y="264" fill="#000000" font-family="Helvetica" font-size="12px" text-anchor="middle">IPC parent?</text></switch></g><path d="M 230 300 L 230 433.63" fill="none" stroke="#000000" stroke-miterlimit="10" pointer-events="stroke"/><path d="M 230 438.88 L 226.5 431.88 L 230 433.63 L 233.5 431.88 Z" fill="#000000" stroke="#000000" stroke-miterlimit="10" pointer-events="all"/><path d="M 140 260 L 183.63 260" fill="none" stroke="#000000" stroke-miterlimit="10" pointer-events="stroke"/><path d="M 188.88 260 L 181.88 263.5 L 183.63 260 L 181.88 256.5 Z" fill="#000000" stroke="#000000" stroke-miterlimit="10" pointer-events="all"/><rect x="230" y="310" width="40" height="20" fill="none" stroke="none" pointer-events="all"/><g transform="translate(-0.5 -0.5)"><switch><foreignObject style="overflow: visible; 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align-items: unsafe center; justify-content: unsafe center; width: 38px; height: 1px; padding-top: 250px; margin-left: 271px;"><div style="box-sizing: border-box; font-size: 0; text-align: center; "><div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; ">NO</div></div></div></foreignObject><text x="290" y="254" fill="#000000" font-family="Helvetica" font-size="12px" text-anchor="middle">NO</text></switch></g><rect x="360" y="230" width="230" height="200" fill="#f5f5f5" stroke="#666666" pointer-events="all"/><path d="M 270 260 L 460 260 Q 470 260 470 261.82 L 470 263.63" fill="none" stroke="#000000" stroke-miterlimit="10" pointer-events="stroke"/><path d="M 470 268.88 L 466.5 261.88 L 470 263.63 L 473.5 261.88 Z" fill="#000000" stroke="#000000" stroke-miterlimit="10" pointer-events="all"/><path d="M 470 290 L 470 310 L 470 290 L 470 303.63" fill="none" stroke="#000000" stroke-miterlimit="10" pointer-events="stroke"/><path d="M 470 308.88 L 466.5 301.88 L 470 303.63 L 473.5 301.88 Z" fill="#000000" stroke="#000000" stroke-miterlimit="10" pointer-events="all"/><rect x="410" y="270" width="120" height="20" fill="#dae8fc" stroke="#6c8ebf" pointer-events="all"/><g transform="translate(-0.5 -0.5)"><switch><foreignObject style="overflow: visible; text-align: left;" pointer-events="none" width="100%" height="100%" requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"><div xmlns="http://www.w3.org/1999/xhtml" style="display: flex; align-items: unsafe center; justify-content: unsafe center; width: 118px; height: 1px; padding-top: 280px; margin-left: 411px;"><div style="box-sizing: border-box; font-size: 0; text-align: center; "><div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; ">transfer encoding</div></div></div></foreignObject><text x="470" y="284" fill="#000000" font-family="Helvetica" font-size="12px" text-anchor="middle">transfer encoding</text></switch></g><path d="M 470 330 L 470 353.63" fill="none" stroke="#000000" stroke-miterlimit="10" pointer-events="stroke"/><path d="M 470 358.88 L 466.5 351.88 L 470 353.63 L 473.5 351.88 Z" fill="#000000" stroke="#000000" stroke-miterlimit="10" pointer-events="all"/><rect x="410" y="310" width="120" height="20" fill="#f8cecc" stroke="#b85450" pointer-events="all"/><g transform="translate(-0.5 -0.5)"><switch><foreignObject style="overflow: visible; text-align: left;" pointer-events="none" width="100%" height="100%" requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"><div xmlns="http://www.w3.org/1999/xhtml" style="display: flex; align-items: unsafe center; justify-content: unsafe center; width: 118px; height: 1px; padding-top: 320px; margin-left: 411px;"><div style="box-sizing: border-box; font-size: 0; text-align: center; "><div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; ">IPC send</div></div></div></foreignObject><text x="470" y="324" fill="#000000" font-family="Helvetica" font-size="12px" text-anchor="middle">IPC send</text></switch></g><path d="M 470 380 L 470 393.63" fill="none" stroke="#000000" stroke-miterlimit="10" pointer-events="stroke"/><path d="M 470 398.88 L 466.5 391.88 L 470 393.63 L 473.5 391.88 Z" fill="#000000" stroke="#000000" stroke-miterlimit="10" pointer-events="all"/><rect x="410" y="360" width="120" height="20" fill="#f8cecc" stroke="#b85450" pointer-events="all"/><g transform="translate(-0.5 -0.5)"><switch><foreignObject style="overflow: visible; text-align: left;" pointer-events="none" width="100%" height="100%" requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"><div xmlns="http://www.w3.org/1999/xhtml" style="display: flex; align-items: unsafe center; justify-content: unsafe center; width: 118px; height: 1px; padding-top: 370px; margin-left: 411px;"><div style="box-sizing: border-box; font-size: 0; text-align: center; "><div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; ">IPC recv</div></div></div></foreignObject><text x="470" y="374" fill="#000000" font-family="Helvetica" font-size="12px" text-anchor="middle">IPC recv</text></switch></g><path d="M 470 420 L 470 470 L 296.37 470" fill="none" stroke="#000000" stroke-miterlimit="10" pointer-events="stroke"/><path d="M 291.12 470 L 298.12 466.5 L 296.37 470 L 298.12 473.5 Z" fill="#000000" stroke="#000000" stroke-miterlimit="10" pointer-events="all"/><rect x="410" y="400" width="120" height="20" fill="#dae8fc" stroke="#6c8ebf" pointer-events="all"/><g transform="translate(-0.5 -0.5)"><switch><foreignObject style="overflow: visible; text-align: left;" pointer-events="none" width="100%" height="100%" requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"><div xmlns="http://www.w3.org/1999/xhtml" style="display: flex; align-items: unsafe center; justify-content: unsafe center; width: 118px; height: 1px; padding-top: 410px; margin-left: 411px;"><div style="box-sizing: border-box; font-size: 0; text-align: center; "><div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; ">transfer decoding</div></div></div></foreignObject><text x="470" y="414" fill="#000000" font-family="Helvetica" font-size="12px" text-anchor="middle">transfer decoding</text></switch></g><rect x="520" y="230" width="70" height="20" fill="none" stroke="none" pointer-events="all"/><g transform="translate(-0.5 -0.5)"><switch><foreignObject style="overflow: visible; text-align: left;" pointer-events="none" width="100%" height="100%" requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"><div xmlns="http://www.w3.org/1999/xhtml" style="display: flex; align-items: unsafe center; justify-content: unsafe center; width: 68px; height: 1px; padding-top: 240px; margin-left: 521px;"><div style="box-sizing: border-box; font-size: 0; text-align: center; "><div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; ">IPC layer</div></div></div></foreignObject><text x="555" y="244" fill="#000000" font-family="Helvetica" font-size="12px" text-anchor="middle">IPC layer</text></switch></g><rect x="100" y="210" width="40" height="20" fill="#f8cecc" stroke="#b85450" pointer-events="all"/><g transform="translate(-0.5 -0.5)"><switch><foreignObject style="overflow: visible; text-align: left;" pointer-events="none" width="100%" height="100%" requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"><div xmlns="http://www.w3.org/1999/xhtml" style="display: flex; align-items: unsafe center; justify-content: unsafe center; width: 38px; height: 1px; padding-top: 220px; margin-left: 101px;"><div style="box-sizing: border-box; font-size: 0; text-align: center; "><div style="display: inline-block; font-size: 12px; font-family: Helvetica; color: #000000; line-height: 1.2; pointer-events: all; white-space: normal; word-wrap: normal; "><font style="font-size: 11px">C API</font></div></div></div></foreignObject><text x="120" y="224" fill="#000000" font-family="Helvetica" font-size="12px" text-anchor="middle">C API</text></switch></g></g><switch><g requiredFeatures="http://www.w3.org/TR/SVG11/feature#Extensibility"/><a transform="translate(0,-5)" href="https://desk.draw.io/support/solutions/articles/16000042487" target="_blank"><text text-anchor="middle" font-size="10px" x="50%" y="100%">Viewer does not support full SVG 1.1</text></a></switch></svg>
\ No newline at end of file
diff --git a/toolkit/components/glean/docs/dev/index.md b/toolkit/components/glean/docs/dev/index.md
new file mode 100644
index 0000000000..334f040ed9
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/index.md
@@ -0,0 +1,15 @@
+# Developing Firefox on Glean
+
+This section of docs is designed to be helpful to people developing FOG.
+If you're not touching code, tests, or documentation in `toolkit/components/glean`,
+and you're not interested in implementation details, you probably want
+[the user docs instead](../user/index).
+
+```{toctree}
+:titlesonly:
+:maxdepth: 1
+:glob:
+
+*
+Glean SDK Source <https://github.com/mozilla/glean/>
+```
diff --git a/toolkit/components/glean/docs/dev/ipc.md b/toolkit/components/glean/docs/dev/ipc.md
new file mode 100644
index 0000000000..1d6bf5366d
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/ipc.md
@@ -0,0 +1,184 @@
+# Inter-process Communication (IPC)
+
+Firefox Desktop is a multi-process desktop application.
+Code requiring instrumentation may be on any of its processes,
+so FOG provide facilities to do just that.
+
+## Design
+
+The IPC Design of FOG was worked out in
+[bug 1618253](https://bugzilla.mozilla.org/show_bug.cgi?id=1618253).
+
+It centred around a few specific concepts:
+
+### Forbidding Non-Commutative Operations
+
+Because we cannot nicely impose a canonical ordering of metric operations across all processes,
+FOG forbids non-[commutative](https://en.wikipedia.org/wiki/Commutative_property)
+metric operations in some circumstances.
+
+For example,
+`Add()`-ing to a Counter metric works from multiple processes because the order doesn't matter.
+However, given a String metric being `Set()` from multiple processes simultaneously,
+which value should it take?
+
+This ambiguity is not a good foundation to build trust on,
+so we forbid setting a String metric from multiple processes.
+
+#### List of Forbidden Operations
+
+* Boolean's `set` (this is the metric type's only operation)
+* Labeled Boolean's `set` (this is the metric type's only operation)
+* String's `set` (this is the metric type's only operation)
+* Labeled String's `set` (this is the metric type's only operation)
+* String List's `set`
+    * `add` is permitted (order and uniqueness are not guaranteed)
+* Timespan's `start`, `stop`, and `cancel` (these are the metric type's only operations)
+* UUID's `set` and `generateAndSet` (these are the metric type's only operations)
+* Datetime's `set` (this is the metric type's only operation)
+* Quantity's `set` (this is the metric type's only operation)
+
+This list may grow over time as new metric types are added.
+If there's an operation/metric type on this list that you need to use in a non-parent process,
+please reach out
+[on the #glean channel](https://chat.mozilla.org/#/room/#glean:mozilla.org)
+and we'll help you out.
+
+### Process Agnosticism
+
+For metric types that can be used cross-process,
+FOG provides no facility for identifying which process the instrumentation is on.
+
+What this means is that if you accumulate to a
+[Timing Distribution](https://mozilla.github.io/glean/book/user/metrics/timing_distribution.html)
+in multiple processes,
+all the samples from all the processes will be combined in the same metric.
+
+If you wish to distinguish samples from different process types,
+you will need multiple metrics and inline code to select the proper one for the given process.
+For example:
+
+```C++
+if (XRE_GetProcessType() == GeckoProcessType_Default) {
+  mozilla::glean::performance::cache_size.Accumulate(numBytes / 1024);
+} else {
+  mozilla::glean::performance::non_main_process_cache_size.Accumulate(numBytes / 1024);
+}
+```
+
+### Scheduling
+
+FOG makes no guarantee about when non-main-process metric values are sent across IPC.
+FOG will try its best to schedule opportunistically in idle moments,
+and during orderly shutdowns.
+
+There are a few cases where we provide more firm guarantees:
+
+#### Tests
+
+There are test-only APIs in Rust, C++, and Javascript.
+These do not await a flush of child process metric values.
+You can use the test-only method `testFlushAllChildren` on the `FOG`
+XPCOM component to await child data's arrival:
+```js
+await Services.fog.testFlushAllChildren();
+```
+See [the test documentation](testing.md) for more details on testing FOG.
+For writing tests about instrumentation, see
+[the instrumentation test documentation](../user/instrumentation_tests).
+
+#### Pings
+
+We do not guarantee that non-main-process data has made it into a specific ping.
+
+[Built-in pings](https://mozilla.github.io/glean/book/user/pings/index.html)
+are submitted by the Rust Glean SDK at times FOG doesn't directly control,
+so there may be data not present in the parent process when a built-in ping is submitted.
+We don't anticipate this causing a problem since child-process data that
+"misses" a given ping will be included in the next one.
+
+At this time,
+[Custom Pings](https://mozilla.github.io/glean/book/user/pings/custom.html)
+must be sent in the parent process and have no mechanism
+to schedule their submission for after child-process data arrives in the parent process.
+[bug 1732118](https://bugzilla.mozilla.org/show_bug.cgi?id=1732118)
+tracks the addition of such a mechanism or guarantee.
+
+#### Shutdown
+
+We will make a best effort during an orderly shutdown to flush all pending data in child processes.
+This means a disorderly shutdown (usually a crash)
+may result in child process data being lost.
+
+#### Size
+
+We don't measure or keep an up-to-date calculation of the size of the IPC Payload.
+We do, however, keep a count of the number of times the IPC Payload has been accessed.
+This is used as a (very) conservative estimate of the size of the IPC Payload so we do not exceed the
+[IPC message size limit](https://searchfox.org/mozilla-central/search?q=kMaximumMessageSize).
+
+See [bug 1745660](https://bugzilla.mozilla.org/show_bug.cgi?id=1745660).
+
+### Mechanics
+
+The rough design is that the parent process can request an immediate flush of pending data,
+and each child process can decide to flush its pending data whenever it wishes.
+The former is via `FlushFOGData() returns (ByteBuf)` and the latter via  `FOGData(ByteBuf)`.
+
+Pending Data is a buffer of bytes generated by `bincode` in Rust in the Child,
+handed off to C++, passed over IPC,
+then given back to `bincode` in Rust on the Parent.
+
+Rust is then responsible for turning the pending data into
+[metrics API][glean-metrics] calls on the metrics in the parent process.
+
+#### Supported Process Types
+
+FOG supports messaging between the following types of child process and the parent process:
+* content children (via `PContent`
+  (for now. See [bug 1641989](https://bugzilla.mozilla.org/show_bug.cgi?id=1641989))
+* gmp children (via `PGMP`)
+* gpu children (via `PGPU`)
+* rdd children (via `PRDD`)
+* socket children (via `PSocketProcess`)
+* utility children (via `PUtilityProcess`)
+
+See
+[the process model docs](/dom/ipc/process_model.rst)
+for more information about what that means.
+
+### Adding Support for a new Process Type
+
+Adding support for a new process type is a matter of extending the two messages
+mentioned above in "Mechanics" to another process type's protocol (ipdl file).
+
+1. Add two messages to the appropriate sections in `P<ProcessType>.ipdl`
+    * (( **Note:** `PGPU` _should_ be the only ipdl where `parent`
+      means the non-parent/-main/-UI process,
+      but double-check that you get this correct.))
+    * Add `async FOGData(ByteBuf&& aBuf);` to the parent/main/UI process side of things
+      (most often `parent:`).
+    * Add `async FlushFOGData() returns (ByteBuf buf);` to the non-parent/-main/-UI side
+      (most often `child:`).
+2. Implement the protocol endpoints in `P<ProcessType>{Child|Parent}.{h|cpp}`
+    * The message added to the `parent: ` section goes in
+      `P<ProcessType>Parent.{h|cpp}` and vice versa.
+3. Add to `FOGIPC.cpp`'s `FlushAllChildData` code that
+    1. Enumerates all processes of the newly-supported type (there may only be one),
+    2. Calls `SendFlushFOGData on each, and
+    3. Adds the resulting promise to the array.
+4. Add to `FOGIPC.cpp`'s `SendFOGData` the correct `GeckoProcessType_*`
+   enum value, and appropriate code for getting the parent process singleton and calling
+   `SendFOGData` on it.
+5. Add to the fog crate's `register_process_shutdown` function
+   handling for at-shutdown flushing of IPC data.
+   If this isn't added, we will log (but not panic)
+   on the first use of Glean APIs on an unsupported process type.
+    * "Handling" might be an empty block with a comment explaining where to find it
+      (like how `PROCESS_TYPE_DEFAULT` is handled)
+    * Or it might be custom code
+      (like `PROCESS_TYPE_CONTENT`'s)
+6. Add to the documented [list of supported process types](#supported-process-types)
+   the process type you added support for.
+
+[glean-metrics]: https://mozilla.github.io/glean/book/reference/metrics/index.html
diff --git a/toolkit/components/glean/docs/dev/jog.md b/toolkit/components/glean/docs/dev/jog.md
new file mode 100644
index 0000000000..c8d0549cd4
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/jog.md
@@ -0,0 +1,91 @@
+# Runtime Metric Definition Subsystem: JOG
+
+```{admonition} I'm Sorry
+Why is it caled JOG? Because it's concerned with... run... time.
+```
+
+The normal mechanism for registering metrics,
+for reasons as varied from ease-of-impl to performance,
+happens at compile time.
+However, this doesn't support use cases like
+* [Artifact Builds][artifact-build]
+  (Where only the JavaScript of Firefox Desktop is repackaged at build time,
+  so there is no compile environment)
+* Dynamic Telemetry
+  (A theorized system for instrumenting Firefox Desktop without shipping code)
+* Web Extensions
+  (Or at least the kind that can't or won't use
+  [the Glean JS SDK][glean-js])
+
+Thus we need a subsystem that supports the runtime registration of metrics.
+We call it JOG and it was implemented in [bug 1698184][impl-bug].
+
+## JavaScript Only
+
+Metrics in C++ and Rust are identified by identifiers which we can't swap out at runtime.
+Thus, in order for changes to metrics to be visible to instrumented systems in C++ or Rust, you must compile.
+
+JavaScript, on the other hand, we supply instances to on-demand.
+It not only supports the specific use cases driving this project,
+it's the only environment that can benefit from runtime metric definition in Firefox Desktop.
+
+## Design
+
+The original design was done as part of
+[bug 1662863][design-bug].
+Things have mostly just been refined from there.
+
+## Architecture
+
+We silo as much of the subsystem as we can into the
+`jog` module located in `toolkit/components/glean/bindings/jog/`.
+This includes the metrics construction factory and storage for metrics instances and their names and ids.
+
+Unfortunately, so that the metrics instances can be accessed by FFI,
+the Rust metrics instances created by the `jog` crate are stored within the `fog` crate.
+
+Speaking of FFI, the `jog` crate is using cbindgen to be accessible to C++.
+
+If necessary or pleasant, it is probably possible to do away with the C++ storage,
+moving the category set and metrics id map to Rust and moving information over FFI as needed.
+
+Test methods are run from `nsIFOG` (so we can use them in JS in xpcshell)
+to static `JOG::` functions.
+
+### Build Integration
+
+If JOG detects we're an artifact build (by checking `MOZ_ARTIFACT_BUILDS`),
+it generates `jogfile.json` and ensures it is placed in `GreD`
+(next to the `firefox` binary).
+
+`jogfile.json` includes only the metric and ping information necessary to register them at runtime.
+(It doesn't know about tags or descriptions, just the shapes and names of things)
+
+This file is read the first time JS tries to get a metric category from the
+`Glean` global or a ping from the `GleanPings` global.
+
+Yes, this is on the main thread. Yes, this is synchronous. Yes, this is file I/O.
+
+Since this is a developer build, we think this is worth it to support Artifact Builds.
+
+If we're wrong about this and there are additional conditions we should place JOG under,
+please [contact us][glean-channel].
+
+#### If things get weird, delete `objdir/dist/bin/jogfile.json`
+
+Sometimes, metrics or pings you've added may not appear when you run Firefox.
+For these and other odd cases, the solution is the same:
+delete `jogfile.json` from the `dist/bin` directory of your objdir, then try again.
+
+This shouldn't happen if you keep your artifact and non-artifact objdirs segregated
+(as is good practice).
+
+If, despite doing things properly you still see this or something else odd, then that's a bug.
+Please [file it in Toolkit :: Telemetry][file-bug]
+
+[artifact-build]: https://firefox-source-docs.mozilla.org/contributing/build/artifact_builds.html
+[glean-js]: https://mozilla.github.io/glean/book/user/adding-glean-to-your-project/javascript.html
+[impl-bug]: https://bugzilla.mozilla.org/show_bug.cgi?id=1698184
+[design-bug]: https://bugzilla.mozilla.org/show_bug.cgi?id=1662863
+[glean-channel]: https://chat.mozilla.org/#/room/#glean:mozilla.org
+[file-bug]: https://bugzilla.mozilla.org/enter_bug.cgi?assigned_to=nobody%40mozilla.org&bug_ignored=0&bug_severity=--&bug_status=NEW&bug_type=defect&cf_a11y_review_project_flag=---&cf_fx_iteration=---&cf_fx_points=---&cf_performance_impact=---&cf_status_firefox106=---&cf_status_firefox107=---&cf_status_firefox108=---&cf_status_firefox_esr102=---&cf_status_thunderbird_esr102=---&cf_status_thunderbird_esr91=---&cf_tracking_firefox106=---&cf_tracking_firefox107=---&cf_tracking_firefox108=---&cf_tracking_firefox_esr102=---&cf_tracking_firefox_relnote=---&cf_tracking_thunderbird_esr102=---&cf_tracking_thunderbird_esr91=---&cf_webcompat_priority=---&component=Telemetry&contenttypemethod=list&contenttypeselection=text%2Fplain&defined_groups=1&filed_via=standard_form&flag_type-203=X&flag_type-37=X&flag_type-41=X&flag_type-607=X&flag_type-721=X&flag_type-737=X&flag_type-787=X&flag_type-799=X&flag_type-800=X&flag_type-803=X&flag_type-846=X&flag_type-855=X&flag_type-864=X&flag_type-930=X&flag_type-936=X&flag_type-937=X&flag_type-952=X&form_name=enter_bug&maketemplate=Remember%20values%20as%20bookmarkable%20template&op_sys=Unspecified&priority=--&product=Toolkit&rep_platform=Unspecified&short_desc=Problem%20with%20JOG%3A%20&target_milestone=---&version=unspecified
diff --git a/toolkit/components/glean/docs/dev/local_glean.md b/toolkit/components/glean/docs/dev/local_glean.md
new file mode 100644
index 0000000000..046cf6e79c
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/local_glean.md
@@ -0,0 +1,100 @@
+# Developing with a local Glean build
+
+FOG uses a release version of Glean, as published on [crates.io][cratesio-glean].
+
+For local development and try runs you can replace this Glean implementation with a local or remote version.
+
+1. To tell `mach` where to find your Glean, patch the [top-level `Cargo.toml`][cargo-toml]. E.g. like this:
+
+    ```toml
+    [patches.crates-io]
+    glean = { git = "https://github.com/myfork/glean", branch = "my-feature-branch" }
+    glean-core = { git = "https://github.com/myfork/glean", branch = "my-feature-branch" }
+    ```
+
+    Both crates are required to ensure they are in sync.
+
+    You can specify the exact code to use by `branch`, `tag` or `rev` (Git commit).
+    See the [cargo documentation for details][cargo-doc].
+
+    You can also use a path dependency:
+
+    ```toml
+    [patches.crates-io]
+    glean = { path = "../glean/glean-core/rlb" }
+    glean-core = { path = "../glean/glean-core" }
+    ```
+
+2. If the crate version in the patched repository is not
+   [semver]-compatible with the version required by the
+   `fog` and `fog_control` crates,
+   you need to change the version in the following files to match the ones in your
+   `glean` repo:
+
+    ```
+    toolkit/components/glean/Cargo.toml
+    toolkit/components/glean/api/Cargo.toml
+    ```
+
+    This tells FOG's crates that it needs your local Glean's version.
+
+3. Update the Cargo lockfile:
+
+    ```
+    cargo update -p glean
+    ```
+
+4.  Mozilla's supply-chain management policy requires that third-party software
+    (which includes the Glean SDK because it is distributed as though it is third-party)
+    be audited and certified as safe.
+    Your local Glean SDK probably hasn't been vetted. If you try to vendor right now,
+    `./mach vendor rust` will complain something like:
+
+    ```
+    Vet error: There are some issues with your policy.audit-as-crates-io entries
+    ```
+
+    This is because your local Glean SDK is neither of a version nor is from a source that has been vetted.
+    To allow your local Glean crates to be treated as crates.io-sourced crates for vetting,
+    add the following sections to the top of `supply-chain/config.toml`:
+
+    ```toml
+    [policy.glean]
+    audit-as-crates-io = true
+
+    [policy.glean-core]
+    audit-as-crates-io = true
+    ```
+
+    If your local Glean is of a non-vetted version, you can update `glean` and
+    `glean-core`'s entries in `supply-chain/audits.toml` to the version you're using.
+    If you don't, `./mach vendor rust` will complain and not complete.
+
+    **Note:** Do not attempt to check these changes in.
+    These changes bypass supply chain defenses.
+    `@supply-chain-reviewers` may become cross as they `r-` your patch.
+
+5. Vendor the changed crates:
+
+    ```
+    ./mach vendor rust
+    ```
+
+    **Note:** If you're using a path dependency, `mach vendor rust` doesn't actually change files.
+    Instead it pulls the files directly from the location on disk you specify.
+
+6. Finally, build Firefox:
+
+    ```
+    ./mach build
+    ```
+
+A remote reference works for try runs as well,
+but a path dependency will not.
+
+Please ensure to not land a non-release version of Glean.
+
+[cratesio-glean]: https://crates.io/crates/glean
+[cargo-toml]: https://searchfox.org/mozilla-central/rev/f07a609a76136ef779c65185165ff5ac513cc172/Cargo.toml#76
+[cargo-doc]: https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#specifying-dependencies-from-git-repositories
+[semver]: https://semver.org/
diff --git a/toolkit/components/glean/docs/dev/new_metric_types.md b/toolkit/components/glean/docs/dev/new_metric_types.md
new file mode 100644
index 0000000000..a3bcdc8b54
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/new_metric_types.md
@@ -0,0 +1,285 @@
+# Adding a New Metric Type
+
+This document covers how to add a new metric type to FOG.
+You should only have to do this if a new metric type is added to the
+[Glean SDK](https://mozilla.github.io/glean/book/user/metrics/index.html)
+and it is needed in Firefox Desktop.
+
+## IPC
+
+For detailed information about the IPC design,
+including a list of forbidden operations,
+please consult
+[the FOG IPC documentation](ipc.md).
+
+When adding a new metric type, the main IPC considerations are:
+* Which operations are forbidden because they are not commutative?
+    * Most `set`-style operations cannot be reconciled sensibly across multiple processes.
+* If there are non-forbidden operations,
+what partial representation will this metric have in non-main processes?
+Put another way, what shape of storage will this take up in the
+[IPC Payload](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/api/src/ipc.rs)?
+    * For example, Counters can aggregate all partial counts together to a single
+    "partial sum". So
+    [its representation](https://searchfox.org/mozilla-central/rev/803b368879fa332e8e2c1840bf1ec164f7ed2c32/toolkit/components/glean/api/src/ipc.rs#45)
+    in the IPC Payload is just a single number per Counter.
+    * In contrast, Timing Distributions' bucket arrangements are known only to the core,
+    so it can't combine sample counts in child processes.
+    Instead we record durations in the highest resolution (nanos),
+    and send a stream of high-precision samples across IPC.
+
+To implement IPC support in a metric type,
+we split FOG's Rust implementation of the metric into three pieces:
+1. An umbrella `enum` with the name `MetricTypeMetric`.
+    * It has a `Child` and a `Parent` variant.
+    * It is IPC-aware and is responsible for
+        * If on a non-parent-process,
+        either storing partial representations in the IPC Payload,
+        or logging errors if forbidden non-test APIs are called.
+        (Or panicking if test APIs are called.)
+        * If on the parent process, dispatching API calls on its inner Rust Language Binding metric.
+2. The parent-process implementation is supplied by
+   [the RLB](https://crates.io/crates/glean/).
+    * For testing, it stores the `MetricId` that identifies this particular metric in a cross-process fashion.
+    * For testing, it exposes a `child_metric()` function to create its `Child` equivalent.
+    * For testing and if it supports operations in a non-parent-process,
+      it exposes a `metric_id()` function to access the stored `MetricId`.
+3. The `MetricTypeIpc` is the non-parent-process implementation.
+    * If it does support operations in non-parent processes it stores the
+      `MetricId` that identifies this particular metric in a cross-process fashion.
+
+## Mirrors
+
+FOG can mirror Glean metrics to Telemetry probes via the
+[Glean Interface For Firefox Telemetry](../user/gifft.md).
+
+Can this metric type be mirrored?
+Should it be mirrored?
+
+If so, add an appropriate Telemetry probe for it to mirror to,
+documenting the compatibility in
+[the GIFFT docs](../user/gifft.md).
+
+### GIFFT Tests
+
+If you add a GIFFT mirror, don't forget to test that the mirror works.
+You should be able to do this by adding a task to
+[`toolkit/components/glean/tests/xpcshell/test_GIFFT.js`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/tests/xpcshell/test_GIFFT.js).
+
+### GIFFT C++ State: Typical Locking and Shutdown
+
+Some metric types (`labeled_*`, `timespan`, `timing_distribution`)
+require holding state in C++ to make GIFFT work.
+Pings also hold state to support `testBeforeNextSubmit()`.
+If your new metric type requires state in C++,
+the current state-of-the-art is a `StaticDataMutex`-locked `UniquePtr` to a `nsTHashTable`.
+Access to the inner map is guarded by the lock and is controlled and lazily-instantiated through a single access function.
+[See Ping's `GetCallbackMapLock()`](https://searchfox.org/mozilla-central/source/toolkit/components/glean/bindings/private/Ping.cpp)
+for example.
+
+It is important to clear this state to avoid leaks.
+(See [bug 1752417](https://bugzilla.mozilla.org/show_bug.cgi?id=1752417).)
+However, instrumentation may call metrics APIs at any time.
+
+Therefore, GIFFT explicitly stops supporting these state-requiring operations after the
+[`AppShutdownTelemetry` shutdown phase](https://searchfox.org/mozilla-central/source/xpcom/base/ShutdownPhase.h).
+This is because during the next phase (`XPCOMWillShutdown`) we clear the state.
+
+## Rust
+
+FOG uses the Rust Language Binding APIs (the `glean` crate) with a layer of IPC on top.
+
+The IPC additions and glean-core trait implementations are in the
+[`private` module of the `fog` crate](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/api/src/metrics).
+
+Each metric type gets its own file, mimicking the structure in
+[`glean_core`](https://github.com/mozilla/glean/tree/main/glean-core/src/metrics)
+and [`glean`](https://github.com/mozilla/glean/tree/main/glean-core/rlb/src/private).
+Unless, of course, that metric is a labeled metric type.
+Then the sub metric type gets its own file,
+and you need to add "Labeledness" to it by implementing
+`Sealed` for your new type following the pattern in
+[`api/src/private/labeled.rs`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/api/src/private/labeled.rs).
+
+Every method on the metric type is public for now,
+including test methods,
+and is at least all the methods exposed via the
+[metric traits](https://github.com/mozilla/glean/tree/main/glean-core/src/traits).
+
+To support IPC and the MLA FFI (see below)
+we identify metric instances by MetricId and store them in maps in
+[the `__glean_metric_maps` mod of `metrics.rs`](https://hg.mozilla.org/mozilla-central/toolkit/components/glean/api/src/metrics.rs).
+This work is done by the `rust.py` and `rust(_pings).jinja2` extensions to `glean_parser` found
+[in the `build_scripts/glean_parser_ext/` folder](https://searchfox.org/mozilla-central/source/toolkit/components/glean/build_scripts/glean_parser_ext).
+
+You shouldn't have to edit these files for new metric types,
+as the original modifications to `glean_parser` for this type should already be generating correct code.
+
+### Rust Tests
+
+You should be able to smoke test the basic functionality in Rust unit tests.
+You can do this within the metric type implementation file directly.
+
+## C++ and JS
+
+The C++ and JS APIs are implemented [atop the Rust API](code_organization.md).
+We treat them both together since, though they're different languages,
+they're both implemented in C++ and share much of their implementation.
+
+The overall design is to build the C++ API atop the Multi-Language Architecture's
+(MLA's) FFI, then build the JS API atop the C++ API.
+This allows features like the
+[Glean Interface For Firefox Telemetry (GIFFT)](../user/gifft.md)
+that target only C++ and JS to be more simply implemented in the C++ layer.
+Exceptions to this (where the JS uses the FFI directly) are discouraged.
+
+Each metric type has six pieces you'll need to cover:
+
+### 1. MLA FFI
+
+- Using our convenient macros,
+  define the metric type's Multi-Language Architecture FFI layer above the Rust API in
+  [`api/src/ffi/`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/api/src/ffi/).
+
+### 2. C++ Impl
+
+- Implement a type called `XMetric` (e.g. `CounterMetric`) in `mozilla::glean::impl` in
+  [`bindings/private/`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/bindings/private/).
+    - Its methods should be named the same as the ones in the Rust API, transformed to `CamelCase`.
+    - They should all be public.
+    - Multiplex the FFI's `test_have` and `test_get` functions into a single
+      `TestGetValue` function that returns a
+      `mozilla::Maybe` wrapping the C++ type that best fits the metric type.
+- Include the new metric type in
+  [`bindings/MetricTypes.h`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/bindings/MetricTypes.h).
+- Include the new files in
+  [`moz.build`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/moz.build).
+  The header file should be added to `EXPORTS.mozilla.glean.bindings` and the
+  `.cpp` file should be added to `UNIFIED_SOURCES`.
+
+### 3. IDL
+
+- Duplicate the public API (including its docs) to
+  {searchfox}`dom/webidl/GleanMetrics.webidl`
+  with the name `GleanX` (e.g. `GleanCounter`).
+    - Inherit from `GleanMetric`.
+    - The naming style for methods here is `lowerCamelCase`.
+    - If the metric method is a reserved word, prepend it with a `_`.
+    - Web IDL bindings use
+      [their own mapping for types](/dom/webIdlBindings/index.md).
+      If you choose ones that most closely resemble the C++ types,
+      you'll make your life easier.
+- Add a new mapping in `dom/bindings/Bindings.conf`:
+  ```idl
+  'GleanX': {
+      'nativeType': 'mozilla::glean::GleanX',
+      'headerFile': 'mozilla/glean/bindings/X.h',
+  },
+  ```
+    - If you don't, you will get a build error complaining `fatal error: 'mozilla/dom/GleanX.h' file not found`.
+
+### 4. JS Impl
+
+- Implement the `GleanX` (e.g. `GleanCounter`) type
+  in the same header and `.cpp` as `XMetric` in
+  {searchfox}`toolkit/components/glean/bindings/private/`
+    - It should own an instance of and delegate method implementations to `XMetric`.
+    - In the definition of `GleanX`, member identifiers are back to
+      `CamelCase`.
+    - Test-only methods can throw `DataError` on failure.
+    - Review the [Web IDL Bindings documentation](/dom/webIdlBindings/index.html)
+      for help with optional, nullable, and non-primitive types.
+
+### 6. Tests
+
+Two languages means two test suites.
+
+- Add a never-expiring test-only metric of your type to
+  [`test_metrics.yaml`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/tests/test_metrics.yaml).
+    - Feel free to be clever with the name,
+      but be sure to make clear that it is test-only.
+- **C++ Tests (GTest)** - Add a small test case to
+  [`gtest/TestFog.cpp`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/tests/gtest/TestFog.cpp).
+    - For more details, peruse the [testing docs](testing.md).
+- **JS Tests (xpcshell)** - Add a small test case to
+  [`xpcshell/test_Glean.js`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/tests/xpcshell/test_Glean.js)
+  and
+  [`xpcshell/test_JOG.js`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/tests/xpcshell/test_JOG.js).
+  If your metric type has supported IPC operations, also add cases to the `IPC` variants of these test files.
+    - For more details, peruse the [testing docs](testing.md).
+
+### 7. API Documentation
+
+Metric API Documentation is centralized in
+[the Glean SDK Book](https://mozilla.github.io/glean/book/user/metrics/index.html).
+
+You will need to craft a Pull Request against
+[the SDK](https://github.com/mozilla/glean/)
+adding a C++ and JS example to the specific metric type's API docs.
+
+Add a notice at the top of both examples that these APIs are only available in Firefox Desktop:
+````md
+<div data-lang="C++" class="tab">
+
+> **Note**: C++ APIs are only available in Firefox Desktop.
+
+```cpp
+#include "mozilla/glean/GleanMetrics.h"
+
+mozilla::glean::category_name::metric_name.Api(args);
+```
+
+There are test APIs available too:
+
+```cpp
+#include "mozilla/glean/GleanMetrics.h"
+
+ASSERT_EQ(value, mozilla::glean::category_name::metric_name.TestGetValue().ref());
+```
+</div>
+
+// and again for <div data-lang="JS">
+````
+
+If you're lucky, the Rust API will have already been added.
+Otherwise you'll need to write an example for that one too.
+
+### 8. Labeled metrics (if necessary)
+
+If your new metric type is Labeled, you have more work to do.
+I'm assuming you've already implemented the non-labeled sub metric type following the steps above.
+Now you must add "Labeledness" to it.
+
+There are four pieces to this:
+
+#### FFI
+
+- To add the writeable storage Rust will use to store the dynamically-generated sub metric instances,
+  add your sub metric type's map as a list item in the `submetric_maps` `mod` of
+  [`rust.jinja2`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/build_scripts/glean_parser_ext/templates/rust.jinja2).
+- Following the pattern of the others, add a `fog_{your labeled metric name here}_get()` FFI API to
+  `api/src/ffi/mod.rs`.
+  This is what C++ and JS will use to allocate and retrieve sub metric instances by id.
+
+#### C++
+
+- Following the pattern of the others, add a template specialiation for `Labeled<YourSubMetric>::Get` to
+  [`bindings/private/Labeled.cpp`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/bindings/private/Labeled.cpp).
+  This will ensure C++ consumers can fetch or create sub metric instances.
+
+#### JS
+
+- Already handled for you since the JS types all inherit from `GleanMetric`
+  and the JS template knows to add your new type to `NewSubMetricFromIds(...)`
+  (see `GleanLabeled::NamedGetter` if you're curious).
+
+#### Tests
+
+- The labeled variant will need tests the same as Step #6.
+  A tip: be sure to test two labels with different values.
+
+## Python Tests
+
+We have a suite of tests for ensuring code generation generates appropriate code.
+You should add a metric to [that suite](testing.md) for your new metric type.
+You will need to regenerate the expected files.
diff --git a/toolkit/components/glean/docs/dev/preferences.md b/toolkit/components/glean/docs/dev/preferences.md
new file mode 100644
index 0000000000..732e25c5c9
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/preferences.md
@@ -0,0 +1,105 @@
+# Preferences and Defines
+
+## User Preferences
+
+`datareporting.healthreport.uploadEnabled`
+
+This determines whether the Glean SDK is enabled.
+It can be controlled by users via `about:preferences#privacy`.
+If this is set to false from true, we send a
+["deletion-request" ping](https://mozilla.github.io/glean/book/user/pings/deletion_request.html)
+and no data collections will be persisted or reported from that point.
+
+## Test-only Preferences
+
+`telemetry.fog.test.localhost_port`
+
+If set to a value `port` which is greater than 0, pings will be sent to
+`http://localhost:port` instead of `https://incoming.telemetry.mozilla.org`.
+If set to a value `port` which is less than 0, FOG will:
+1) Tell Glean that upload is enabled, even if it isn't.
+2) Take all pings scheduled for upload and drop them on the floor,
+   telling the Glean SDK that it was sent successfully.
+
+This is how you emulate "recording enabled but upload disabled"
+like developer builds have in Firefox Telemetry.
+When switching from `port < 0` to `port >= 0`,
+Glean will be told (if just temporarily) that upload is disabled.
+This clears the stores of recorded-but-not-reported data.
+Defaults to 0.
+
+`telemetry.fog.test.activity_limit`
+`telemetry.fog.test.inactivity_limit`
+
+This pair of prefs control the length of time of activity before inactivity
+(or vice versa)
+needed before FOG informs the SDK's Client Activity API that the client was (in)active.
+Present to allow testing without figuring out how to mock Rust's clock.
+Their values are integer seconds.
+Defaults to 120 (activity), 1200 (inactivity).
+
+## Internal Preferences
+
+`telemetry.fog.artifact_build`
+
+Read-only. This pref is `true` only if `MOZ_ARTIFACT_BUILDS` was set during configure.
+If true, [JOG](./jog) is enabled so that artifact builds will exhibit changes to their Glean metrics.
+
+## Defines
+
+`MOZ_AUTOMATION`
+
+If set, and `GLEAN_SOURCE_TAGS` isn't set, FOG will set a
+[Glean source tag](https://mozilla.github.io/glean/book/reference/debug/sourceTags.html)
+of `automation`.
+
+If `GLEAN_SOURCE_TAGS` is set, the `automation` source tag will not be added automatically.
+
+If not set, any tags set by `GLEAN_SOURCE_TAGS` will be present.
+
+`MOZ_GLEAN_ANDROID`
+
+If set, the Glean SDK is assumed to be managed by something other than FOG, meaning:
+* [GIFFT][gifft] is disabled.
+* FOG doesn't initialize Glean
+* FOG doesn't relay (in)activity or experiment annotations to Glean
+
+`MOZILLA_OFFICIAL`
+
+If unset, we set a `glean_disable_upload` Rust feature in
+`gkrust` and `gkrust-shared` which is forwarded to `fog_control` as `disable_upload`.
+This feature defaults FOG to an "upload disabled"
+mode where collection on the client proceeds as normal but no ping is sent.
+This mode can be overridden at runtime in two ways:
+* If the ping has a
+  [Debug Tag](https://mozilla.github.io/glean/book/user/debugging/index.html)
+  then it is sent so that it may be inspected in the
+  [Glean Debug Ping Viewer](https://debug-ping-preview.firebaseapp.com/).
+* If the preference `telemetry.fog.test.localhost_port` is set to a value greater than 0,
+  then pings are sent to a server operating locally at that port
+  (even if the ping has a Debug Tag), to enable testing.
+
+`MOZILLA_OFFICIAL` tends to be set on most builds released to users,
+including builds distributed by Linux distributions.
+It tends to not be set on local developer builds.
+See [bug 1680025](https://bugzilla.mozilla.org/show_bug.cgi?id=1680025) for details.
+
+`MOZ_ARTIFACT_BUILDS`
+
+If `MOZ_ARTIFACT_BUILDS` is set in the build config,
+[JOG](./jog) will generate a file for the runtime-registration of metrics and pings.
+This is to support [Artifact Builds](/contributing/build/artifact_builds).
+
+See also `telemetry.fog.artifact_build`.
+
+`OS_TARGET`
+
+If not set to `'Android'` we set a `glean_million_queue` Rust feature
+([see gkrust-features.mozbuild][gkrust-features])
+which, when passed to the Glean SDK,
+opts us into a preinit queue that doesn't discard tasks until there are 10^6 of them.
+
+See [bug 1797494](https://bugzilla.mozilla.org/show_bug.cgi?id=1797494) for details.
+
+[gkrust-features]: https://searchfox.org/mozilla-central/source/toolkit/library/rust/gkrust-features.mozbuild
+[gifft]: ../user/gifft
diff --git a/toolkit/components/glean/docs/dev/storage.md b/toolkit/components/glean/docs/dev/storage.md
new file mode 100644
index 0000000000..00464c6173
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/storage.md
@@ -0,0 +1,14 @@
+# Storage
+
+Both FOG and the Glean SDK require some storage in the
+[Firefox Profile Directory](https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Multiple_profiles).
+
+## FOG
+
+At present FOG's storage is limited to its [preferences](preferences.md).
+
+## Glean SDK
+
+The Glean SDK stores things in the
+[Glean Data Directory](https://mozilla.github.io/glean/book/dev/core/internal/directory-structure.html)
+which can be found at `<profile_dir>/datareporting/glean`.
diff --git a/toolkit/components/glean/docs/dev/style_guide.md b/toolkit/components/glean/docs/dev/style_guide.md
new file mode 100644
index 0000000000..d96766da9f
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/style_guide.md
@@ -0,0 +1,49 @@
+# FOG Documentation Style Guide
+
+FOG's Documentation is written in Markdown.
+You can find its source at `toolkit/components/glean/docs`.
+
+## Line breaks
+
+We will use [semantic linefeeds]:
+* Break anywhere before 80-100 characters
+* Break after any punctuation when it makes sense
+* Break before or after any markdown when it makes sense
+
+**Tip:** To keep lines narrow, use markdown's [reference link]
+feature whenever it makes sense (or all the time. Up to you.).
+
+## Linking to other documentation
+
+Linking to other external documentation is [easy][reference link].
+Linking to other pieces of documentation in the source docs requires a
+link to the source file in the sphinx tree.
+
+Links can be relative e.g. to link to the [preferences] docs:
+
+```md
+[preferences](preferences.md)
+```
+
+Or they can be absolute e.g. to link to the [Telemetry] docs:
+```md
+[Telemetry](/toolkit/components/telemetry/index.rst)
+```
+
+Sphinx will automagically transform that to an
+appropriately-base-url'd url with a `.html` suffix.
+
+
+## Use of "Main" versus "Parent" for processes
+
+When talking about Glean, it is helpeful to distinguish when we are on the main
+process specifically. This is because there is only one main process, and there is only one Glean.
+However, "parent" is a relative term, and it may refer to a process
+that is the parent of another process, but is not itself the main process.
+Prefer use of "main" when it is accurate.
+
+[semantic linefeeds]: https://rhodesmill.org/brandon/2012/one-sentence-per-line/
+[reference link]: https://spec.commonmark.org/0.29/#reference-link
+[Telemetry]: /toolkit/components/telemetry/index.rst
+[#firefox-source-docs:mozilla.org]: https://chat.mozilla.org/#/room/#firefox-source-docs:mozilla.org
+[bug 1621950]: https://bugzilla.mozilla.org/show_bug.cgi?id=1621950
diff --git a/toolkit/components/glean/docs/dev/testing.md b/toolkit/components/glean/docs/dev/testing.md
new file mode 100644
index 0000000000..fe6c3e0fe7
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/testing.md
@@ -0,0 +1,240 @@
+# Testing
+
+```{admonition} This documentation is about testing FOG itself
+This document contains information about how FOG tests itself,
+how to add new tests, how and what to log, and stuff like that.
+If you're interested in learning how to test instrumentation you added,
+you'll want to read
+[the instrumetnation testing docs](../user/instrumentation_tests) instead.
+```
+
+Given the multiple API languages, processes, and dependencies,
+testing FOG is a matter of choosing the right tool for the situation.
+
+## One Big Command
+
+To run all the things, here's the tl;dr:
+
+`./mach build && ./mach lint -W -w -o --fix
+&& ./mach rusttests && ./mach gtest "FOG*"
+&& python3 ./mach python-test toolkit/components/glean/tests/pytest
+&& ./mach test toolkit/components/glean/tests/xpcshell
+&& ./mach telemetry-tests-client toolkit/components/telemetry/tests/marionette/tests/client/test_fog* --gecko-log "-"
+&& ./mach test toolkit/components/glean/tests/browser
+`
+
+## Logging
+
+An often-overlooked first line of testing is "what do the logs say?".
+To turn on logging for FOG, use any of the following:
+* Run Firefox with `RUST_LOG="fog_control,fog,glean_core"`.
+    * On some platforms this will use terminal colours to indicate log level.
+* Run Firefox with `MOZ_LOG="timestamp,sync,glean::*:5,fog::*:5,fog_control::*:5,glean_core::*:5"`.
+* Set the following prefs:
+    * `logging.config.timestamp` to `true`
+    * `logging.config.sync` to `true`
+    * `logging.fog_control::*` to `5`
+    * `logging.fog::*` to `5`
+    * `logging.glean::*` to `5`
+    * `logging.glean_core::*` to `5`
+    * `logging.config.clear_on_startup` to `false` (or all these prefs will be cleared on startup)
+
+For more information on logging in Gecko, see the
+[Gecko Logging docs](/xpcom/logging).
+
+User-destined logs (of the "You did something wrong" variety) might output to the
+[Browser Console](/devtools-user/browser_console/index)
+if they originate in JS land. Open via
+<kbd>Ctrl</kbd>+<kbd>Shift</kbd>+<kbd>J</kbd>, or
+<kbd>Cmd</kbd>+<kbd>Shift</kbd>+<kbd>J</kbd>.
+
+```{admonition} Note
+At present, Rust logging in non-main processes just doesn't work.
+```
+
+### What to log, and to where?
+
+FOG covers a lot a ground (languages, layers):
+where you are determines what logging you have available.
+
+Here are some common situtations for logging:
+
+#### JS to C++
+
+If your logging is aimed at the user using the JS API
+(e.g. because the type provided isn't convertable to the necessary C++ type)
+then use the Browser Console via
+[FOG's Common's `LogToBrowserConsole`](https://searchfox.org/mozilla-central/rev/d107bc8aeadcc816ba85cb21c1a6a1aac1d4ef9f/toolkit/components/glean/bindings/private/Common.cpp#19).
+
+#### C++
+
+If you are in C++ and didn't come from JS, use `MOZ_LOG` with module `fog`.
+
+#### Rust
+
+Use the logging macros from `log`, e.g. `log::info!` or `log::error!`.
+Remember that, no matter the log level, `log::debug!` and `log::trace!`
+[will not appear in non-debug builds](/testing-rust-code/index.md#gecko-logging)
+
+If you are logging due to a situation caused by and fixable by a developer using the API,
+use `log::error!(...)`. Otherwise, use a quieter level.
+
+## `about:glean`
+
+`about:glean` is a page in a running Firefox that allows you to
+[debug the Glean SDK](https://mozilla.github.io/glean/book/user/debugging/index.html)
+in Firefox Desktop.
+It does this through the displayed user interface (just follow the instructions).
+
+## Linting
+
+To keep in accordance with Mozilla's various and several Coding Styles,
+we rely on `mach lint`.
+
+To lint the code in the "usual" way, automatically fixing where possible, run:
+`./mach lint -W -w -o --fix`
+
+This should keep you from checking in code that will automatically be backed out.
+
+## Rust
+
+Not all of our Rust code can be tested in a single fashion, unfortunately.
+
+### Using `rusttests` (Treeherder symbol `Br` (a build task))
+
+If the crate you're testing has no Gecko symbols you can write standard
+[Rust tests](https://doc.rust-lang.org/book/ch11-01-writing-tests.html).
+
+This supports both unit tests
+(inline in the file under test) and integration tests
+(in the `tests/` folder in the crate root).
+Metric type tests are currently written as unit tests inline in the file,
+as they require access to the metric ID, which should only be exposed in tests.
+
+To run FOG's `rusttests` suite use `mach rusttests`
+
+If the crate uses only a few Gecko symbols, they may use the
+`with_gecko` feature to conditionally use them.
+This allows the crate to test its non-Gecko-adjacent code using Rust tests.
+(You will need to cover the Gecko-adjacent code via another means.)
+
+**Note:** Some FOG rusttests panic on purpose. They print stack traces to stdout.
+If the rusttests fail and you see a stack trace,
+double-check it isn't from a purposefully-panicking test.
+
+**Note:** If a test fails, it is very likely they'll poison the test lock.
+This will cause all subsequent tests that attempt to take the test lock
+(which is all of them)
+to also fail due to `PoisonError`s. They can be safely ignored.
+
+### Using `gtest` (Treeherder symbol `GTest` (a build task))
+
+Because Gecko symbols aren't built for the
+`rusttests` build,
+any test that is written for code that uses Gecko symbols should be written as a
+[`gtest`](https://github.com/google/googletest)
+in `toolkit/components/glean/tests/gtest/`.
+You can write the actual test code in Rust.
+It needs to be accompanied by a C++ GTest that calls a C FFI-exported Rust function.
+See [Testing & Debugging Rust Code](/testing-rust-code/index.md) for more.
+See [`toolkit/components/glean/tests/gtest/TestFog.cpp`](https://searchfox.org/mozilla-central/source/toolkit/components/glean/tests/gtest/TestFog.cpp)
+and [`toolkit/components/glean/tests/gtest/test.rs`](https://searchfox.org/mozilla-central/source/toolkit/components/glean/tests/gtest/test.rs)
+for an example.
+
+By necessity these can only be integration tests against the compiled crate.
+
+**Note:** When adding a new test file, don't forget to add it to
+`toolkit/components/glean/tests/gtest/moz.build` and use the
+`FOG` prefix in your test names
+(e.g. `TEST(FOG, YourTestName) { ... }`).
+
+To run FOG's Rust `gtest` suite use `mach gtest FOG.*`
+
+## Python (Treeherder symbol `py3(fp)` aka `source-test-python-fog`)
+
+The [Glean Parser](https://github.com/mozilla/glean_parser/)
+has been augmented to generate FOG-specific APIs for Glean metrics.
+This augmentation is tested by running:
+
+`mach test toolkit/components/glean/tests/pytest`
+
+These tests require Python 3+.
+If your default Python is Python 2, you may need to instead run:
+
+`python3 mach python-test toolkit/components/glean/tests/pytest`
+
+These tests check the code generator output against known good file contents.
+If you change the code generator the files will need an update.
+Run the test suite with the `UPDATE_EXPECT` environment variable set to do that automatically:
+
+`UPDATE_EXPECT=1 mach test toolkit/components/glean/tests/pytest`
+
+## C++ (Treeherder symbol `GTest` (a build task))
+
+To test the C++ parts of FOG's implementation
+(like metric types)
+you should use `gtest`.
+FOG's `gtest` tests are in
+[`gtest/`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/tests/gtest/).
+
+You can either add a test case to an existing file or add a new file.
+If you add a new file, remember to add it to the
+[`moz.build`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/tests/gtest/moz.build))
+or the test runner won't be able to find it.
+
+All tests should start with `FOG` so that all tests are run with
+`./mach gtest FOG*`.
+
+## JS (Treeherder symbol `X(Xn)` for some number `n`)
+
+To test the JS parts of FOG's implementation
+(like metric types)
+you should use `xpcshell`.
+FOG's `xpcshell` tests are in
+[`xpcshell/`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/tests/xpcshell).
+
+You can either add a test case to an existing file or add a new file.
+If you add a new file, remember to add it to the
+[`xpcshell.ini`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/tests/xpcshell/xpcshell.ini)
+or the test runner will not be able to find it.
+
+To run FOG's JS tests, run:
+`./mach test toolkit/components/glean/tests/xpcshell`
+
+## Non-content-process multiprocess (Browser Chrome Mochitests with Treeherder symbol `M(bcN)` for some number `N`)
+
+To test e.g. the GPU process support you need a full Firefox browser:
+xpcshell doesn't have the flexibility.
+To test that and have access to privileged JS (i.e. `Glean` and `FOG` APIs),
+we use browser-chrome-flavoured mochitests you can find in
+[`browser/`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/tests/browser).
+
+If you need to add a new test file, remember to add it to the
+[`browser.ini`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/glean/tests/browser/browser.ini)
+manifest, or the test runner will not be able to find it.
+
+To run FOG's browser chrome tests, run:
+`./mach test toolkit/components/glean/tests/browser`
+
+## Integration (Marionette, borrowing `telemetry-tests-client` Treeherder symbol `tt(c)`)
+
+To test pings (See [bug 1681742](https://bugzilla.mozilla.org/show_bug.cgi?id=1681742))
+or anything that requires one or more full browsers running,
+we use the `telemetry-tests-client` suite in
+[`toolkit/components/telemetry/tests/marionette/tests/client/`](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/telemetry/tests/marionette/tests/client/).
+
+For more information on this suite, look to
+[Firefox Telemetry's Test Documentation](https://firefox-source-docs.mozilla.org/toolkit/components/telemetry/internals/tests.html#integration-tests-telemetry-tests-client-and-telemetry-integration-tests)
+and
+[Marionette's Documentation](/testing/marionette/Testing.md).
+
+To run these integration tests, run:
+`./mach telemetry-tests-client toolkit/components/telemetry/tests/marionette/tests/client/`
+
+To capture the Firefox under test's logs, use the `--gecko-log` parameter.
+For example, to echo to stdout:
+`./mach telemetry-tests-client toolkit/components/telemetry/tests/marionette/tests/client/test_fog* --gecko-log "-"`
+
+**Note:** Running the `tt(c)` suite in this way ignored skip directives in the manifest.
+This means that you might run tests that are not expected to succeed on your platform.
+Check `toolkit/components/telemetry/tests/marionette/tests/client/manifest.ini` for details.
diff --git a/toolkit/components/glean/docs/dev/updating_parser.md b/toolkit/components/glean/docs/dev/updating_parser.md
new file mode 100644
index 0000000000..4609f76a80
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/updating_parser.md
@@ -0,0 +1,52 @@
+# Updating glean_parser
+
+Project FOG uses the `glean_parser` to generate code from metric definitions.
+It depends on [glean-parser] from pypi.org
+
+[glean-parser]: https://pypi.org/project/glean-parser/
+
+To update the in-tree glean-parser change the version in `third_party/python/requirements.in`,
+then run
+
+```
+./mach vendor python
+```
+
+```{note}
+**Important**: the glean_parser and all of its dependencies must support Python 3.5, as discussed here.
+This is the minimum version supported by mach and installed on the CI images for running tests.
+This is enforced by the version ranges declared in the Python installation manifest.
+```
+
+## Version mismatch of the Python dependencies
+
+The logic for handling version mismatches is very similar to the one for the Rust crates.
+See [Updating the Glean SDK](updating_sdk.md) for details.
+However, updating Python packages also requires to think about Python 3.5 (and Python 2, still) compatibility.
+
+## Keeping versions in sync
+
+The Glean SDK and `glean_parser` are currently released as separate projects.
+However each Glean SDK release requires a specific `glean_parser` version.
+When updating one or the other ensure versions stay compatible.
+You can find the currently used `glean_parser` version in the Glean SDK source tree, e.g. in [sdk_generator.sh].
+
+[sdk_generator.sh]: https://github.com/mozilla/glean/blob/main/glean-core/ios/sdk_generator.sh#L28
+
+## Using a local `glean_parser` development version
+
+To test out a new `glean_parser` in mozilla-central follow these steps:
+
+1. Remove `glean_parser` from the user-wide virtual environment.
+   This can be found in a path like `~/.mozbuild/srcdirs/gecko-f5e3b9c6ded5/_virtualenvs/mach/lib/python3.10/site-packages/glean_parser`
+   Note that the `gecko-f5e3b9c6ded5` part will be different depending on your local checkout.
+   Remove all directories and files mentioning `glean_parser`
+2. Remove `glean_parser` from the build virtual enviromment.
+   This can be found in `$MOZ_OBJDIR/_virtualenvs/common/lib/python3.6/site-packages/glean_parser`.
+   Note that `$MOZ_OBJDIR` depends on your local mozconfig configuration.
+   Remove all directories and files mentioning `glean_parser`
+3. Copy the local `glean_parser` checkout into `third_party/python/glean_parser`.
+   E.g. `cp ~/code/glean_parser $GECKO/third_party/python/glean_parser`.
+
+You should now be able to build `mozilla-central` and it will use the modified `glean_parser`.
+You can make further edits in `$GECKO/third_party/python/glean_parser`.
diff --git a/toolkit/components/glean/docs/dev/updating_sdk.md b/toolkit/components/glean/docs/dev/updating_sdk.md
new file mode 100644
index 0000000000..fafec08d39
--- /dev/null
+++ b/toolkit/components/glean/docs/dev/updating_sdk.md
@@ -0,0 +1,48 @@
+# Updating the Glean SDK
+
+Project FOG uses the Glean SDK published as the [`glean`][glean-crate]
+and [`glean-core`][glean-core] crates on crates.io.
+
+[glean-crate]: https://crates.io/crates/glean
+[glean-core]: https://crates.io/crates/glean-core
+
+These two crates' versions are included in several places in mozilla-central.
+To update them all, you should use the command
+`mach update-glean <version, like "54.1.0">`.
+
+This is a semi-manual process.
+Please pay attention to the output of `mach update-glean` for instructions,
+and follow them closely.
+
+## Version mismatches of Rust dependencies
+
+Other crates that are already vendored might require a different version of the same dependencies that the Glean SDK requires.
+The general strategy for Rust dependencies is to keep one single version of the dependency in-tree
+(see [comment #8 in bug 1591555](https://bugzilla.mozilla.org/show_bug.cgi?id=1591555#c8)).
+This might be hard to do in reality since some dependencies might require tweaks in order to work.
+The following strategy can be followed to decide on version mismatches:
+
+* If the versions only **differ by the patch version**, Cargo will keep the vendored version,
+  unless some other dependency pinned specific patch versions;
+  assuming it doesn’t break the Glean SDK;
+  if it does, follow the next steps;
+* If the version of the **vendored dependency is newer** (greater major or minor version) than the version required by the Glean SDK,
+  [file a bug in the Glean SDK component][glean-bug] to get Glean to require the same version;
+    * You will have to abandon updating the Glean SDK to this version.
+      You will have to wait for Glean SDK to update its dependency and for a new Glean SDK release.
+      Then you will have to update to that new Glean SDK version.
+* If the version of the **vendored dependency is older** (lower major or minor version), consider updating the vendored version to the newer one;
+  seek review from the person who vendored that dependency in the first place;
+  if that is not possible or breaks mozilla-central build, then consider keeping both versions vendored in-tree; please note that this option will probably only be approved for small crates,
+  and will require updating the `TOLERATED_DUPES` list in `mach vendor`
+  (instructions are provided as you go).
+
+## Keeping versions in sync
+
+The Glean SDK and `glean_parser` are currently released as separate projects.
+However each Glean SDK release requires a specific `glean_parser` version.
+When updating one or the other ensure versions stay compatible.
+You can find the currently used `glean_parser` version in the Glean SDK source tree, e.g. in [sdk_generator.sh].
+
+[sdk_generator.sh]: https://github.com/mozilla/glean/blob/main/glean-core/ios/sdk_generator.sh#L28
+[glean-bug]: https://bugzilla.mozilla.org/enter_bug.cgi?product=Data+Platform+and+Tools&component=Glean%3A+SDK&priority=P3&status_whiteboard=%5Btelemetry%3Aglean-rs%3Am%3F%5D