--- a/devtools/client/framework/toolbox.js
+++ b/devtools/client/framework/toolbox.js
@@ -1877,23 +1877,24 @@ Toolbox.prototype = {
       return panel;
     });
   },
 
   _pingTelemetrySelectTool(id, reason) {
     const width = Math.ceil(this.win.outerWidth / 50) * 50;
     const panelName = this.getTelemetryPanelName(id);
     const prevPanelName = this.getTelemetryPanelName(this.currentToolId);
+    const cold = !this.getPanel(id);
 
     this._telemetry.addEventProperties("devtools.main", "enter", panelName, null, {
       "host": this._hostType,
       "width": width,
       "start_state": reason,
       "panel_name": id,
-      "cold": !this.getPanel(id)
+      "cold": cold
     });
 
     // On first load this.currentToolId === undefined so we need to skip sending
     // a devtools.main.exit telemetry event.
     if (this.currentToolId) {
       this._telemetry.recordEvent("devtools.main", "exit", prevPanelName, null, {
         "host": this._hostType,
         "width": width,
@@ -1901,16 +1902,23 @@ Toolbox.prototype = {
         "next_panel": id,
         "reason": reason
       });
     }
 
     const pending = ["host", "width", "start_state", "panel_name", "cold"];
     if (id === "webconsole") {
       pending.push("message_count");
+
+      // Cold webconsole event message_count is handled in
+      // devtools/client/webconsole/new-console-output-wrapper.js
+      if (!cold) {
+        this._telemetry.addEventProperty(
+          "devtools.main", "enter", "webconsole", null, "message_count", 0);
+      }
     }
     this._telemetry.preparePendingEvent(
       "devtools.main", "enter", panelName, null, pending);
     this._telemetry.toolOpened(id);
   },
 
   /**
    * Focus a tool's panel by id

--- a/devtools/client/webconsole/new-console-output-wrapper.js
+++ b/devtools/client/webconsole/new-console-output-wrapper.js
@@ -8,16 +8,17 @@ const dom = require("devtools/client/sha
 const ReactDOM = require("devtools/client/shared/vendor/react-dom");
 const { Provider } = require("devtools/client/shared/vendor/react-redux");
 
 const actions = require("devtools/client/webconsole/actions/index");
 const { createContextMenu } = require("devtools/client/webconsole/utils/context-menu");
 const { configureStore } = require("devtools/client/webconsole/store");
 const { isPacketPrivate } = require("devtools/client/webconsole/utils/messages");
 const { getAllMessagesById, getMessage } = require("devtools/client/webconsole/selectors/messages");
+const Telemetry = require("devtools/client/shared/telemetry");
 
 const EventEmitter = require("devtools/shared/event-emitter");
 const ConsoleOutput = createFactory(require("devtools/client/webconsole/components/ConsoleOutput"));
 const FilterBar = createFactory(require("devtools/client/webconsole/components/FilterBar"));
 const SideBar = createFactory(require("devtools/client/webconsole/components/SideBar"));
 const JSTerm = createFactory(require("devtools/client/webconsole/components/JSTerm"));
 
 let store = null;
@@ -33,16 +34,18 @@ function NewConsoleOutputWrapper(parentN
 
   this.init = this.init.bind(this);
 
   this.queuedMessageAdds = [];
   this.queuedMessageUpdates = [];
   this.queuedRequestUpdates = [];
   this.throttledDispatchPromise = null;
 
+  this._telemetry = new Telemetry();
+
   store = configureStore(this.hud);
 }
 NewConsoleOutputWrapper.prototype = {
   init: function() {
     return new Promise((resolve) => {
       const attachRefToHud = (id, node) => {
         this.hud[id] = node;
       };
@@ -381,16 +384,21 @@ NewConsoleOutputWrapper.prototype = {
       return;
     }
 
     this.throttledDispatchPromise = new Promise(done => {
       setTimeout(() => {
         this.throttledDispatchPromise = null;
 
         store.dispatch(actions.messagesAdd(this.queuedMessageAdds));
+
+        const length = this.queuedMessageAdds.length;
+        this._telemetry.addEventProperty(
+          "devtools.main", "enter", "webconsole", null, "message_count", length);
+
         this.queuedMessageAdds = [];
 
         if (this.queuedMessageUpdates.length > 0) {
           this.queuedMessageUpdates.forEach(({ message, res }) => {
             store.dispatch(actions.networkMessageUpdate(message, null, res));
             this.hud.emit("network-message-updated", res);
           });
           this.queuedMessageUpdates = [];

--- a/devtools/server/actors/webconsole.js
+++ b/devtools/server/actors/webconsole.js
@@ -25,17 +25,16 @@ loader.lazyRequireGetter(this, "StackTra
 loader.lazyRequireGetter(this, "JSPropertyProvider", "devtools/shared/webconsole/js-property-provider", true);
 loader.lazyRequireGetter(this, "Parser", "resource://devtools/shared/Parser.jsm", true);
 loader.lazyRequireGetter(this, "NetUtil", "resource://gre/modules/NetUtil.jsm", true);
 loader.lazyRequireGetter(this, "addWebConsoleCommands", "devtools/server/actors/webconsole/utils", true);
 loader.lazyRequireGetter(this, "CONSOLE_WORKER_IDS", "devtools/server/actors/webconsole/utils", true);
 loader.lazyRequireGetter(this, "WebConsoleUtils", "devtools/server/actors/webconsole/utils", true);
 loader.lazyRequireGetter(this, "EnvironmentActor", "devtools/server/actors/environment", true);
 loader.lazyRequireGetter(this, "EventEmitter", "devtools/shared/event-emitter");
-loader.lazyRequireGetter(this, "Telemetry", "devtools/client/shared/telemetry");
 
 // Overwrite implemented listeners for workers so that we don't attempt
 // to load an unsupported module.
 if (isWorker) {
   loader.lazyRequireGetter(this, "ConsoleAPIListener", "devtools/server/actors/webconsole/worker-listeners", true);
   loader.lazyRequireGetter(this, "ConsoleServiceListener", "devtools/server/actors/webconsole/worker-listeners", true);
 } else {
   loader.lazyRequireGetter(this, "ConsoleAPIListener", "devtools/server/actors/webconsole/listeners", true);
@@ -71,18 +70,16 @@ function WebConsoleActor(connection, par
   this.dbg = this.parentActor.makeDebugger();
 
   this._netEvents = new Map();
   this._networkEventActorsByURL = new Map();
   this._gripDepth = 0;
   this._listeners = new Set();
   this._lastConsoleInputEvaluation = undefined;
 
-  this._telemetry = new Telemetry();
-
   this.objectGrip = this.objectGrip.bind(this);
   this._onWillNavigate = this._onWillNavigate.bind(this);
   this._onChangedToplevelDocument = this._onChangedToplevelDocument.bind(this);
   EventEmitter.on(this.parentActor, "changed-toplevel-document",
             this._onChangedToplevelDocument);
   this._onObserverNotification = this._onObserverNotification.bind(this);
   if (this.parentActor.isRootActor) {
     Services.obs.addObserver(this._onObserverNotification,
@@ -860,19 +857,16 @@ WebConsoleActor.prototype =
             }
             messages.push(message);
           });
           break;
         }
       }
     }
 
-    this._telemetry.addEventProperty(
-      "devtools.main", "enter", "webconsole", null, "message_count", messages.length);
-
     return {
       from: this.actorID,
       messages: messages,
     };
   },
 
   /**
    * Handler for the "evaluateJSAsync" request. This method evaluates the given