--- a/devtools/shim/devtools-startup-prefs.js
+++ b/devtools/shim/devtools-startup-prefs.js
@@ -15,8 +15,23 @@ pref("devtools.jsonview.enabled", true);
 #ifdef MOZ_DEV_EDITION
 sticky_pref("devtools.theme", "dark");
 #else
 sticky_pref("devtools.theme", "light");
 #endif
 
 // Should the devtools toolbar be opened on startup
 pref("devtools.toolbar.visible", false);
+
+// Pref to drive the devtools onboarding flow experiment. States:
+// - off: forces devtools.enabled to true
+// - on: devtools.enabled is not forced to true.
+// - force: devtools.enabled is not forced to true and cannot be set to true by checking
+//   devtools.selfxss.count. User will have to go through onboarding to use DevTools.
+pref("devtools.onboarding.experiment", "off");
+
+// If devtools.onboarding.experiment is set to "on" or "force", we will flip the
+// devtools.enabled preference to false once. The flag is used to make sure it is only
+// flipped once.
+pref("devtools.onboarding.experiment.flipped", false);
+
+// Flag to check if we already logged the devtools onboarding related probe.
+pref("devtools.onboarding.telemetry.logged", false);

--- a/devtools/shim/devtools-startup.js
+++ b/devtools/shim/devtools-startup.js
@@ -243,26 +243,52 @@ DevToolsStartup.prototype = {
     this.hookWindow(window);
 
     if (Services.prefs.getBoolPref(TOOLBAR_VISIBLE_PREF, false)) {
       // Loading devtools-browser will open the developer toolbar by also checking this
       // pref.
       this.initDevTools();
     }
 
-    if (this.devtoolsFlag) {
-      this.handleDevToolsFlag(window);
-      // This listener is called for all Firefox windows, but we want to execute
-      // that command only once.
-      this.devtoolsFlag = false;
+    // This listener is called for all Firefox windows, but we want to execute some code
+    // only once.
+    if (!this._firstWindowReadyReceived) {
+      this.onFirstWindowReady(window);
+      this._firstWindowReadyReceived = true;
     }
 
     JsonView.initialize();
   },
 
+  onFirstWindowReady(window) {
+    if (this.devtoolsFlag) {
+      this.handleDevToolsFlag(window);
+    }
+
+    // Wait until we get a window before sending a ping to telemetry to avoid slowing down
+    // the startup phase.
+    this.pingOnboardingTelemetry();
+  },
+
+  /**
+   * Check if the user is being flagged as DevTools users or not. This probe should only
+   * be logged once per profile.
+   */
+  pingOnboardingTelemetry() {
+    // Only ping telemetry once per profile.
+    let alreadyLoggedPref = "devtools.onboarding.telemetry.logged";
+    if (Services.prefs.getBoolPref(alreadyLoggedPref)) {
+      return;
+    }
+
+    let scalarId = "devtools.onboarding.is_devtools_user";
+    Services.telemetry.scalarSet(scalarId, this.isDevToolsUser());
+    Services.prefs.setBoolPref(alreadyLoggedPref, true);
+  },
+
   /**
    * Register listeners to all possible entry points for Developer Tools.
    * But instead of implementing the actual actions, defer to DevTools codebase.
    * In most cases, it only needs to call this.initDevTools which handles the rest.
    * We do that to prevent loading any DevTools module until the user intent to use them.
    */
   hookWindow(window) {
     // Key Shortcuts need to be added on all the created windows.
@@ -442,24 +468,45 @@ DevToolsStartup.prototype = {
   /**
    * Depending on some runtime parameters (command line arguments as well as existing
    * preferences), the DEVTOOLS_ENABLED_PREF might be forced to true.
    *
    * @param {Boolean} hasDevToolsFlag
    *        true if any DevTools command line argument was passed when starting Firefox.
    */
   setupEnabledPref(hasDevToolsFlag) {
+    // Read the current experiment state.
+    let experimentState = Services.prefs.getCharPref("devtools.onboarding.experiment");
+    let isRegularExperiment = experimentState == "on";
+    let isForcedExperiment = experimentState == "force";
+    let isInExperiment = isRegularExperiment || isForcedExperiment;
+
+    // Force devtools.enabled to true for users that are not part of the experiment.
+    if (!isInExperiment) {
+      Services.prefs.setBoolPref(DEVTOOLS_ENABLED_PREF, true);
+      return;
+    }
+
+    // Force devtools.enabled to false once for each experiment user.
+    if (!Services.prefs.getBoolPref("devtools.onboarding.experiment.flipped")) {
+      Services.prefs.setBoolPref(DEVTOOLS_ENABLED_PREF, false);
+      Services.prefs.setBoolPref("devtools.onboarding.experiment.flipped", true);
+    }
+
     if (Services.prefs.getBoolPref(DEVTOOLS_ENABLED_PREF)) {
       // Nothing to do if DevTools are already enabled.
       return;
     }
 
-    let hasToolbarPref = Services.prefs.getBoolPref(TOOLBAR_VISIBLE_PREF, false);
+    // We only consider checking the actual isDevToolsUser() if the user is in the
+    // "regular" experiment group.
+    let isDevToolsUser = isRegularExperiment && this.isDevToolsUser();
 
-    if (hasDevToolsFlag || hasToolbarPref || this.isDevToolsUser()) {
+    let hasToolbarPref = Services.prefs.getBoolPref(TOOLBAR_VISIBLE_PREF, false);
+    if (hasDevToolsFlag || hasToolbarPref || isDevToolsUser) {
       Services.prefs.setBoolPref(DEVTOOLS_ENABLED_PREF, true);
     }
   },
 
   hookKeyShortcuts(window) {
     let doc = window.document;
     let keyset = doc.createElement("keyset");
     keyset.setAttribute("id", "devtoolsKeyset");

--- a/toolkit/components/telemetry/Scalars.yaml
+++ b/toolkit/components/telemetry/Scalars.yaml
@@ -951,16 +951,29 @@ devtools.aboutdevtools:
       Number of times the user left about:devtools without enabling devtools.
     expires: "60"
     kind: uint
     notification_emails:
       - dev-developer-tools@lists.mozilla.org, jdescottes@mozilla.com
     record_in_processes:
       - 'main'
 
+devtools.onboarding:
+  is_devtools_user:
+    bug_numbers:
+      - 1408339
+    description: >
+      How many users are flagged as existing devtools users.
+    expires: "60"
+    kind: boolean
+    notification_emails:
+      - dev-developer-tools@lists.mozilla.org, jdescottes@mozilla.com
+    record_in_processes:
+      - 'main'
+
 navigator.storage:
   estimate_count:
     bug_numbers:
       - 1359708
     description: >
       Number of times navigator.storage.estimate has been used.
     expires: "60"
     kind: uint