--- a/devtools/shim/devtools-startup-prefs.js
+++ b/devtools/shim/devtools-startup-prefs.js
@@ -16,14 +16,22 @@ pref("devtools.jsonview.enabled", true);
 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);
 
-// Flag to drive the devtools onboarding flow experiment. Forces devtools.enabled to true
-// when false.
-pref("devtools.onboarding.experiment", 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
@@ -468,30 +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;
     }
 
-    if (!Services.prefs.getBoolPref("devtools.onboarding.experiment")) {
-      // Force devtools.enabled to true for users that are not part of the experiment.
-      Services.prefs.setBoolPref(DEVTOOLS_ENABLED_PREF, true);
-      return;
-    }
+    // We only consider checking the actual isDevToolsUser() if the user is in the
+    // "regular" experiment group.
+    let isDevToolsUser = isRegularExperiment && this.isDevToolsUser();
 
     let hasToolbarPref = Services.prefs.getBoolPref(TOOLBAR_VISIBLE_PREF, false);
-
-    if (hasDevToolsFlag || hasToolbarPref || this.isDevToolsUser()) {
+    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");