diff --git a/dom/base/nsFocusManager.cpp b/dom/base/nsFocusManager.cpp
index b9c9173ec57e..531dccd1acf8 100644
--- a/dom/base/nsFocusManager.cpp
+++ b/dom/base/nsFocusManager.cpp
@@ -734,6 +734,11 @@ nsFocusManager::WindowRaised(mozIDOMWindowProxy* aWindow) {
     // ATOK, so we need to do it here.
     BrowserParent::UnsetTopLevelWebFocusAll();
     ActivateOrDeactivate(window, true);
+
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    if (obs) {
+      obs->NotifyObservers(aWindow, "window-raised", nullptr);
+    }
   }
 
   // retrieve the last focused element within the window that was raised
@@ -816,6 +821,11 @@ nsFocusManager::WindowLowered(mozIDOMWindowProxy* aWindow) {
   // is called.
   if (XRE_IsParentProcess()) {
     ActivateOrDeactivate(window, false);
+
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    if (obs) {
+      obs->NotifyObservers(aWindow, "window-lowered", nullptr);
+    }
   }
 
   // keep track of the window being lowered, so that attempts to raise the
diff --git a/toolkit/components/telemetry/Histograms.json b/toolkit/components/telemetry/Histograms.json
index 7a98e7bb72e8..b90149d6d37b 100644
--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -15386,5 +15386,18 @@
     "bug_numbers": [1647876],
     "description": "Seconds between `user-interaction-active` and `user-interaction-inactive`. For use in evaluating baseline engagement for Project FOG.",
     "releaseChannelCollection": "opt-out"
+  },
+  "FOG_EVAL_WINDOW_RAISED_S" : {
+    "products": ["firefox"],
+    "record_in_processes": ["main"],
+    "alert_emails": ["chutten@mozilla.com"],
+    "expires_in_version": "85",
+    "kind": "exponential",
+    "keyed": false,
+    "high": 7200,
+    "n_buckets": 50,
+    "bug_numbers": [1647876],
+    "description": "Seconds between a Firefox window being raised and lowered. For use in evaluating baseline engagement for Project FOG.",
+    "releaseChannelCollection": "opt-out"
   }
 }
diff --git a/toolkit/components/telemetry/Scalars.yaml b/toolkit/components/telemetry/Scalars.yaml
index afa0039eead4..22f3cc1b0a66 100644
--- a/toolkit/components/telemetry/Scalars.yaml
+++ b/toolkit/components/telemetry/Scalars.yaml
@@ -5002,6 +5002,22 @@ fog.eval:
     record_in_processes:
       - 'main'
 
+  window_raised:
+    bug_numbers:
+      - 1647876
+    description: >
+      Whether a Firefox window is presently raised.
+      For use in evaluating baseline engagement for Project FOG.
+    expires: '85'
+    kind: 'boolean'
+    notification_emails:
+      - 'chutten@mozilla.com'
+    release_channel_collection: 'opt-out'
+    products:
+      - 'firefox'
+    record_in_processes:
+      - 'main'
+
   user_active_error:
     bug_numbers:
       - 1647876
@@ -5020,6 +5036,24 @@ fog.eval:
     record_in_processes:
       - 'main'
 
+  window_raised_error:
+    bug_numbers:
+      - 1647876
+    description: >
+      How many Telemetry stopwatch errors did we have while trying to measure window raising?
+      These could be attempts to start a started timer or finish an unstarted timer or so forth.
+      See Stopwatch::Start and Stopwatch::Finish for details.
+      For use in evaluating baseline engagement for Project FOG.
+    expires: '85'
+    kind: 'uint'
+    notification_emails:
+      - 'chutten@mozilla.com'
+    release_channel_collection: 'opt-out'
+    products:
+      - 'firefox'
+    record_in_processes:
+      - 'main'
+
 # The following section is for probes testing the Telemetry system. They will not be
 # submitted in pings and are only used for testing.
 telemetry.test:
diff --git a/toolkit/components/telemetry/pings/TelemetrySession.jsm b/toolkit/components/telemetry/pings/TelemetrySession.jsm
index 56b646510a23..550b2c5dae16 100644
--- a/toolkit/components/telemetry/pings/TelemetrySession.jsm
+++ b/toolkit/components/telemetry/pings/TelemetrySession.jsm
@@ -856,6 +856,9 @@ var Impl = {
     // Attach the active-ticks related observers.
     this.addObserver("user-interaction-active");
     this.addObserver("user-interaction-inactive");
+    // For FOG Engagement Evaluation, attach window observers.
+    this.addObserver("window-raised");
+    this.addObserver("window-lowered");
   },
 
   /**
@@ -1146,6 +1149,24 @@ var Impl = {
     return this.send(REASON_TEST_PING);
   },
 
+  /**
+   * Instruments window raises and lowers during a Telemetry Session.
+   */
+  _onWindowChange(aWindow, aRaised) {
+    Telemetry.scalarSet("fog.eval.window_raised", aRaised);
+    let error = false;
+    if (aRaised) {
+      error = !TelemetryStopwatch.start("FOG_EVAL_WINDOW_RAISED_S", aWindow, {
+        inSeconds: true,
+      });
+    } else {
+      error = !TelemetryStopwatch.finish("FOG_EVAL_WINDOW_RAISED_S", aWindow);
+    }
+    if (error) {
+      Telemetry.scalarAdd("fog.eval.window_raised_error", 1);
+    }
+  },
+
   /**
    * Tracks the number of "ticks" the user was active in.
    */
@@ -1255,6 +1276,12 @@ var Impl = {
       case "user-interaction-inactive":
         this._onActiveTick(false);
         break;
+      case "window-raised":
+        this._onWindowChange(aSubject, true);
+        break;
+      case "window-lowered":
+        this._onWindowChange(aSubject, false);
+        break;
     }
     return undefined;
   },