--- a/accessible/base/NotificationController.cpp
+++ b/accessible/base/NotificationController.cpp
@@ -607,16 +607,18 @@ NotificationController::ProcessMutationE
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // NotificationCollector: private
 
 void
 NotificationController::WillRefresh(mozilla::TimeStamp aTime)
 {
+  Telemetry::AutoTimer<Telemetry::A11Y_TREE_UPDATE_TIMING_MS> timer;
+
   AUTO_PROFILER_LABEL("NotificationController::WillRefresh", OTHER);
 
   // If the document accessible that notification collector was created for is
   // now shut down, don't process notifications anymore.
   NS_ASSERTION(mDocument,
                "The document was shut down while refresh observer is attached!");
   if (!mDocument)
     return;

--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -38,16 +38,26 @@
     "kind": "exponential",
     "high": 60000,
     "n_buckets": 20,
     "keyed": false,
     "description": "The amount of time the parent process blocked while detecting a UIA client.",
     "bug_numbers": [1423989],
     "alert_emails": ["dbolter@mozilla.com"]
   },
+  "A11Y_TREE_UPDATE_TIMING_MS" : {
+    "record_in_processes": ["main", "content"],
+    "alert_emails": ["asurkov@mozilla.com"],
+    "bug_numbers": [1424768],
+    "expires_in_version": "never",
+    "description": "The amount of time taken to update the accessibility tree (ms)",
+    "kind" : "exponential",
+    "high": 60000,
+    "n_buckets": 50
+  },
   "ADDON_CONTENT_POLICY_SHIM_BLOCKING_LOADING_MS": {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "58",
     "kind": "exponential",
     "high": 60000,
     "n_buckets": 20,
     "keyed": true,
     "description": "The amount of time the content process blocked processing shouldLoad shims for an add-on (keyed by add-on ID) prior to the load event, for each document load.",