diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index bf2ff30a11a5..7b76b339899b 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -1141,8 +1141,11 @@ nsDocumentViewer::PermitUnloadInternal(bool *aShouldPrompt,
     nsIDocument::PageUnloadingEventTimeStamp timestamp(mDocument);
 
     mInPermitUnload = true;
-    EventDispatcher::DispatchDOMEvent(window, nullptr, event, mPresContext,
-                                      nullptr);
+    {
+      Telemetry::AutoTimer<Telemetry::HANDLE_BEFOREUNLOAD_MS> telemetryTimer;
+      EventDispatcher::DispatchDOMEvent(window, nullptr, event, mPresContext,
+                                        nullptr);
+    }
     mInPermitUnload = false;
   }
 
@@ -1325,7 +1328,10 @@ nsDocumentViewer::PageHide(bool aIsUnload)
 
     nsIDocument::PageUnloadingEventTimeStamp timestamp(mDocument);
 
-    EventDispatcher::Dispatch(window, mPresContext, &event, nullptr, &status);
+    {
+      Telemetry::AutoTimer<Telemetry::HANDLE_UNLOAD_MS> telemetryTimer;
+      EventDispatcher::Dispatch(window, mPresContext, &event, nullptr, &status);
+    }
   }
 
 #ifdef MOZ_XUL
diff --git a/toolkit/components/telemetry/Histograms.json b/toolkit/components/telemetry/Histograms.json
index 13ddf9186f08..31969719408d 100644
--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -10374,5 +10374,23 @@
     "high": 300000,
     "n_buckets": 30,
     "description": "Time in MS that content is narrated in 10 second increments up to 5 minutes"
+  },
+  "HANDLE_UNLOAD_MS": {
+    "alert_emails": ["kchen@mozilla.com"],
+    "expires_in_version": "55",
+    "kind": "exponential",
+    "high": 10000,
+    "n_buckets": 50,
+    "bug_numbers": [1301346],
+    "description": "The time spent handling unload event in milliseconds. It measures all documents and subframes separately. If there are multiple handlers for the unload event in a document, this will record a single value across all handlers in the document."
+  },
+  "HANDLE_BEFOREUNLOAD_MS": {
+    "alert_emails": ["kchen@mozilla.com"],
+    "expires_in_version": "55",
+    "kind": "exponential",
+    "high": 10000,
+    "n_buckets": 50,
+    "bug_numbers": [1301346],
+    "description": "The time spent handling beforeunload event in milliseconds. It measures all documents and subframes separately. If there are multiple handlers for the unload event in a document, this will record a single value across all handlers in the document."
   }
 }