--- a/devtools/client/inspector/inspector.js
+++ b/devtools/client/inspector/inspector.js
@@ -843,16 +843,19 @@ Inspector.prototype = {
       this.eyeDropperButton = null;
     }
   },
 
   /**
    * Reset the inspector on new root mutation.
    */
   onNewRoot: function () {
+    // Record new-root timing for telemetry
+    this._newRootStart = this.panelWin.performance.now();
+
     this._defaultNode = null;
     this.selection.setNodeFront(null);
     this._destroyMarkup();
     this.isDirty = false;
 
     let onNodeSelected = defaultNode => {
       // Cancel this promise resolution as a new one had
       // been queued up.
@@ -895,16 +898,28 @@ Inspector.prototype = {
 
     // Wait for full expand of the selected node in order to ensure
     // the markup view is fully emitted before firing 'reloaded'.
     // 'reloaded' is used to know when the panel is fully updated
     // after a page reload.
     yield onExpand;
 
     this.emit("reloaded");
+
+    // Record the time between new-root event and inspector fully loaded.
+    if (this._newRootStart) {
+      // Only log the timing when inspector is not destroyed and is in foreground.
+      if (this.toolbox && this.toolbox.currentToolId == "inspector") {
+        let delay = this.panelWin.performance.now() - this._newRootStart;
+        let telemetryKey = "DEVTOOLS_INSPECTOR_NEW_ROOT_TO_RELOAD_DELAY_MS";
+        let histogram = Services.telemetry.getHistogramById(telemetryKey);
+        histogram.add(delay);
+      }
+      delete this._newRootStart;
+    }
   }),
 
   _selectionCssSelector: null,
 
   /**
    * Set the currently selected node unique css selector.
    * Will store the current target url along with it to allow pre-selection at
    * reload

--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -8441,16 +8441,26 @@
     "bug_numbers": [1405585],
     "expires_in_version": "62",
     "kind": "exponential",
     "high": 120000,
     "n_buckets": 100,
     "keyed": true,
     "description": "Time taken (in ms) to update DevTools panel when reloading a page. This is keyed by tool ID being currently opened [inspector, webconsole, jsdebugger, styleeditor, shadereditor, canvasdebugger, performance, memory, netmonitor, storage, webaudioeditor, scratchpad, dom]."
   },
+  "DEVTOOLS_INSPECTOR_NEW_ROOT_TO_RELOAD_DELAY_MS": {
+    "record_in_processes": ["main"],
+    "alert_emails": ["dev-developer-tools@lists.mozilla.org", "hkirschner@mozilla.com"],
+    "bug_numbers": [1405585],
+    "expires_in_version": "62",
+    "kind": "exponential",
+    "high": 120000,
+    "n_buckets": 100,
+    "description": "Time taken (in ms) to update the inspector during a page reload, starting from new-root event."
+  },
   "DEVTOOLS_DEBUGGER_DISPLAY_SOURCE_LOCAL_MS": {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "never",
     "kind": "exponential",
     "high": 10000,
     "n_buckets": 1000,
     "description": "The time (in milliseconds) that it took to display a selected source to the user."
   },