--- a/devtools/client/framework/toolbox.js
+++ b/devtools/client/framework/toolbox.js
@@ -9,16 +9,17 @@ const SOURCE_MAP_WORKER = "resource://de
 const MAX_ORDINAL = 99;
 const SPLITCONSOLE_ENABLED_PREF = "devtools.toolbox.splitconsoleEnabled";
 const SPLITCONSOLE_HEIGHT_PREF = "devtools.toolbox.splitconsoleHeight";
 const DISABLE_AUTOHIDE_PREF = "ui.popup.disable_autohide";
 const HOST_HISTOGRAM = "DEVTOOLS_TOOLBOX_HOST";
 const SCREENSIZE_HISTOGRAM = "DEVTOOLS_SCREEN_RESOLUTION_ENUMERATED_PER_USER";
 const CURRENT_THEME_SCALAR = "devtools.current_theme";
 const HTML_NS = "http://www.w3.org/1999/xhtml";
+const REGEX_PANEL = /webconsole|inspector|jsdebugger|styleeditor|netmonitor|storage/;
 
 var {Ci, Cc} = require("chrome");
 var promise = require("promise");
 var defer = require("devtools/shared/defer");
 var Services = require("Services");
 var ChromeUtils = require("ChromeUtils");
 var {gDevTools} = require("devtools/client/framework/devtools");
 var EventEmitter = require("devtools/shared/event-emitter");
@@ -1874,30 +1875,39 @@ Toolbox.prototype = {
       this.emit("select", id);
       this.emit(id + "-selected", panel);
       return panel;
     });
   },
 
   _pingTelemetrySelectTool(id, reason) {
     const width = Math.ceil(this.win.outerWidth / 50) * 50;
-
-    let panelName = id;
-    if (!/webconsole|inspector|jsdebugger|styleeditor|netmonitor|storage/.test(id)) {
-      panelName = "other";
-    }
+    const panelName = this.getTelemetryPanelName(id);
+    const prevPanelName = this.getTelemetryPanelName(this.currentToolId);
 
     this._telemetry.addEventProperties("devtools.main", "enter", panelName, null, {
       "host": this._hostType,
       "width": width,
       "start_state": reason,
       "panel_name": id,
       "cold": !this.getPanel(id)
     });
 
+    // 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,
+        "panel_name": prevPanelName,
+        "next_panel": id,
+        "reason": reason
+      });
+    }
+
     const pending = ["host", "width", "start_state", "panel_name", "cold"];
     if (id === "webconsole") {
       pending.push("message_count");
     }
     this._telemetry.preparePendingEvent(
       "devtools.main", "enter", panelName, null, pending);
     this._telemetry.toolOpened(id);
   },
@@ -2802,22 +2812,32 @@ Toolbox.prototype = {
     this.toolbarButtons.forEach(button => {
       if (typeof button.teardown == "function") {
         // teardown arguments have already been bound in _createButtonState
         button.teardown();
       }
     });
 
     // We need to grab a reference to win before this._host is destroyed.
-    let win = this.win;
+    const win = this.win;
+    const host = this._getTelemetryHostString();
+    const width = Math.ceil(win.outerWidth / 50) * 50;
+    const prevPanelName = this.getTelemetryPanelName(this.currentToolId);
 
     this._telemetry.toolClosed("toolbox");
     this._telemetry.recordEvent("devtools.main", "close", "tools", null, {
-      host: this._getTelemetryHostString(),
-      width: Math.ceil(win.outerWidth / 50) * 50
+      host: host,
+      width: width
+    });
+    this._telemetry.recordEvent("devtools.main", "exit", prevPanelName, null, {
+      "host": host,
+      "width": width,
+      "panel_name": this.currentToolId,
+      "next_panel": "none",
+      "reason": "toolbox_close"
     });
     this._telemetry.destroy();
 
     // Finish all outstanding tasks (which means finish destroying panels and
     // then destroying the host, successfully or not) before destroying the
     // target.
     deferred.resolve(settleAll(outstanding)
         .catch(console.error)
@@ -3218,9 +3238,16 @@ Toolbox.prototype = {
    * as active for the toolbox and has its related devtools about:config preference set
    * to true.
    * @see browser/components/extensions/ext-devtools.js
    */
   isWebExtensionEnabled: function(extensionUUID) {
     let extInfo = this._webExtensions.get(extensionUUID);
     return extInfo && Services.prefs.getBoolPref(extInfo.pref, false);
   },
+
+  getTelemetryPanelName: function(id) {
+    if (!REGEX_PANEL.test(id)) {
+      return "other";
+    }
+    return id;
+  }
 };

--- a/toolkit/components/telemetry/Events.yaml
+++ b/toolkit/components/telemetry/Events.yaml
@@ -198,8 +198,22 @@ devtools.main:
     expiry_version: never
     extra_keys:
       host: "Toolbox host (positioning): bottom, side, window or other."
       width: Toolbox width rounded up to the nearest 50px.
       message_count: The number of cached console messages.
       start_state: debuggerStatement, breakpoint, exception, tab_switch, toolbox_show, initial_panel, toggle_settings_off, toggle_settings_on, key_shortcut, select_next_key, select_prev_key, tool_unloaded, inspect_dom, unknown etc.
       panel_name: The name of the panel opened, webconsole, inspector, jsdebugger, styleeditor, netmonitor, storage or other
       cold: Is this the first time the current panel has been opened in this toolbox?
+  exit:
+    objects: ["webconsole", "inspector", "jsdebugger", "styleeditor", "netmonitor", "storage", "other"]
+    bug_numbers: [1455270]
+    notification_emails: ["dev-developer-tools@lists.mozilla.org", "hkirschner@mozilla.com"]
+    record_in_processes: ["main"]
+    description: User closes a tool in the devtools toolbox.
+    release_channel_collection: opt-out
+    expiry_version: never
+    extra_keys:
+      host: "Toolbox host (positioning): bottom, side, window or other."
+      width: Toolbox width rounded up to the nearest 50px.
+      next_panel: The name of the panel closed, webconsole, inspector, jsdebugger, styleeditor, netmonitor, storage or other.
+      panel_name: The name of the panel opened, webconsole, inspector, jsdebugger, styleeditor, netmonitor, storage or other
+      reason: debuggerStatement, breakpoint, exception, tab_switch, toolbox_show, initial_panel, toggle_settings_off, toggle_settings_on, key_shortcut, select_next_key, select_prev_key, tool_unloaded, inspect_dom, toolbox_closed, unknown etc.