diff --git a/browser/base/content/test/protectionsUI/browser_protectionsUI_cookies_subview.js b/browser/base/content/test/protectionsUI/browser_protectionsUI_cookies_subview.js
index 0ee1bdab2d30..1346fb94c1d3 100644
--- a/browser/base/content/test/protectionsUI/browser_protectionsUI_cookies_subview.js
+++ b/browser/base/content/test/protectionsUI/browser_protectionsUI_cookies_subview.js
@@ -369,10 +369,6 @@ add_task(async function testCookiesSubViewAllowedHeuristic() {
     TPC_PREF,
     Ci.nsICookieService.BEHAVIOR_REJECT_TRACKER
   );
-  Services.prefs.setBoolPref(
-    "privacy.restrict3rdpartystorage.heuristic.window_open",
-    true
-  );
   let principal =
     Services.scriptSecurityManager.createContentPrincipalFromOrigin(
       // eslint-disable-next-line @microsoft/sdl/no-insecure-url
diff --git a/docshell/test/mochitest/test_form_restoration.html b/docshell/test/mochitest/test_form_restoration.html
index 5ee8a21da7dc..b9292367701e 100644
--- a/docshell/test/mochitest/test_form_restoration.html
+++ b/docshell/test/mochitest/test_form_restoration.html
@@ -21,7 +21,6 @@
     }
 
     async function startTest(aTestFun) {
-      await SimpleTest.enableLegacyUnpartitionedStorage();
       let bc = new BroadcastChannel("form_restoration");
 
       let promise = waitForMessage(bc);
diff --git a/dom/indexedDB/test/file.js b/dom/indexedDB/test/file.js
index 435edc1052bf..f6ed4e451bca 100644
--- a/dom/indexedDB/test/file.js
+++ b/dom/indexedDB/test/file.js
@@ -253,7 +253,7 @@ function grabFileUsageAndContinueHandler(request) {
 
 function getCurrentUsage(usageHandler) {
   let qms = SpecialPowers.Services.qms;
-  let principal = SpecialPowers.wrap(document).effectiveStoragePrincipal;
+  let principal = SpecialPowers.wrap(document).nodePrincipal;
   let cb = SpecialPowers.wrapCallback(usageHandler);
   qms.getUsageForPrincipal(principal, cb);
 }
diff --git a/dom/indexedDB/test/test_sandbox.html b/dom/indexedDB/test/test_sandbox.html
index 61b64596cbf2..0a15a5328786 100644
--- a/dom/indexedDB/test/test_sandbox.html
+++ b/dom/indexedDB/test/test_sandbox.html
@@ -81,7 +81,7 @@ function runInSandbox(sandbox, testFunc) {
 }
 
 // Use the window principal for the sandbox; location.origin is not sufficient.
-var sb = new SpecialPowers.Cu.Sandbox(SpecialPowers.wrap(window.document).effectiveStoragePrincipal,
+var sb = new SpecialPowers.Cu.Sandbox(window,
                                       { wantGlobalProperties: ["indexedDB"] });
 
 sb.ok = SpecialPowers.Cu.exportFunction(ok, sb);
diff --git a/dom/notification/test/mochitest/notification_worker.js b/dom/notification/test/mochitest/notification_worker.js
index de09cc649143..ee9bda30bcc5 100644
--- a/dom/notification/test/mochitest/notification_worker.js
+++ b/dom/notification/test/mochitest/notification_worker.js
@@ -61,26 +61,13 @@ if (self.Notification) {
       // store notification in test context
       this.notification = notification;
 
-      if (self.location.search == "?xorigin") {
-        notification.onerror = function () {
-          ok(true, "onshow handler should be called");
-          done();
-        };
-      } else {
-        notification.onshow = function () {
-          ok(true, "onshow handler should be called");
-          done();
-        };
-      }
+      notification.onshow = function () {
+        ok(true, "onshow handler should be called");
+        done();
+      };
     },
 
     function (done) {
-      if (self.location.search == "?xorigin") {
-        ok(true, "onclose handler can not be called in partitioned workers");
-        done();
-        return;
-      }
-
       var notification = this.notification;
 
       notification.onclose = function () {
diff --git a/dom/notification/test/mochitest/notification_worker_child-child.js b/dom/notification/test/mochitest/notification_worker_child-child.js
index 07e158076308..5179514c6a04 100644
--- a/dom/notification/test/mochitest/notification_worker_child-child.js
+++ b/dom/notification/test/mochitest/notification_worker_child-child.js
@@ -50,28 +50,15 @@ if (self.Notification) {
       // store notification in test context
       this.notification = notification;
 
-      if (self.location.search == "?xorigin") {
-        notification.onerror = function () {
-          ok(true, "onshow handler should be called");
-          done();
-        };
-      } else {
-        notification.onshow = function () {
-          ok(true, "onshow handler should be called");
-          done();
-        };
-      }
+      notification.onshow = function () {
+        ok(true, "onshow handler should be called");
+        done();
+      };
     },
 
     function (done) {
       var notification = this.notification;
 
-      if (self.location.search == "?xorigin") {
-        ok(true, "onclose handler can not be called in partitioned workers");
-        done();
-        return;
-      }
-
       notification.onclose = function () {
         ok(true, "onclose handler should be called");
         done();
diff --git a/dom/notification/test/mochitest/notification_worker_child-parent.js b/dom/notification/test/mochitest/notification_worker_child-parent.js
index b22b7d43b08d..d7f118866fb8 100644
--- a/dom/notification/test/mochitest/notification_worker_child-parent.js
+++ b/dom/notification/test/mochitest/notification_worker_child-parent.js
@@ -7,9 +7,7 @@ function is(a, b, message) {
 }
 
 if (self.Notification) {
-  var child = new Worker(
-    "notification_worker_child-child.js" + self.location.search
-  );
+  var child = new Worker("notification_worker_child-child.js");
   child.onerror = function (e) {
     ok(false, "Error loading child worker " + e);
     postMessage({ type: "finish" });
diff --git a/dom/notification/test/mochitest/test_notification_worker.html b/dom/notification/test/mochitest/test_notification_worker.html
index 20e77b24e3f3..34cf073afd8c 100644
--- a/dom/notification/test/mochitest/test_notification_worker.html
+++ b/dom/notification/test/mochitest/test_notification_worker.html
@@ -20,11 +20,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=916893
   SimpleTest.requestFlakyTimeout("Mock alert service dispatches show and click events.");
 
   async function runTest() {
-    let workerPath = "notification_worker.js";
-    if (isXOrigin) {
-      workerPath += "?xorigin";
-    }
-    var w = new Worker(workerPath);
+    var w = new Worker("notification_worker.js");
     w.onmessage = function(e) {
       if (e.data.type === 'finish') {
         SimpleTest.finish();
diff --git a/dom/notification/test/mochitest/test_notification_worker_child.html b/dom/notification/test/mochitest/test_notification_worker_child.html
index b099840404cb..fb622dc0bfd0 100644
--- a/dom/notification/test/mochitest/test_notification_worker_child.html
+++ b/dom/notification/test/mochitest/test_notification_worker_child.html
@@ -19,11 +19,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=916893
 <script type="text/javascript">
   SimpleTest.requestFlakyTimeout("Mock alert service dispatches show event.");
   async function runTest() {
-    let workerPath = "notification_worker_child-parent.js";
-    if (isXOrigin) {
-      workerPath += "?xorigin";
-    }
-    var w = new Worker(workerPath);
+    var w = new Worker("notification_worker_child-parent.js");
     w.onmessage = function(e) {
       if (e.data.type === 'finish') {
         SimpleTest.finish();
diff --git a/dom/quota/PrincipalUtils.cpp b/dom/quota/PrincipalUtils.cpp
index 291c175b4f7f..b773c9c90ae4 100644
--- a/dom/quota/PrincipalUtils.cpp
+++ b/dom/quota/PrincipalUtils.cpp
@@ -272,7 +272,7 @@ Result<PrincipalMetadata, nsresult> GetInfoFromWindow(
   nsCOMPtr<nsIScriptObjectPrincipal> sop = do_QueryInterface(aWindow);
   QM_TRY(OkIf(sop), Err(NS_ERROR_FAILURE));
 
-  nsCOMPtr<nsIPrincipal> principal = sop->GetEffectiveStoragePrincipal();
+  nsCOMPtr<nsIPrincipal> principal = sop->GetPrincipal();
   QM_TRY(OkIf(principal), Err(NS_ERROR_FAILURE));
 
   return GetInfoFromPrincipal(principal);
@@ -311,7 +311,7 @@ Result<nsAutoCString, nsresult> GetOriginFromWindow(
   nsCOMPtr<nsIScriptObjectPrincipal> sop = do_QueryInterface(aWindow);
   QM_TRY(OkIf(sop), Err(NS_ERROR_FAILURE));
 
-  nsCOMPtr<nsIPrincipal> principal = sop->GetEffectiveStoragePrincipal();
+  nsCOMPtr<nsIPrincipal> principal = sop->GetPrincipal();
   QM_TRY(OkIf(principal), Err(NS_ERROR_FAILURE));
 
   QM_TRY_RETURN(GetOriginFromPrincipal(principal));
diff --git a/layout/base/tests/test_zoom_restore_bfcache.html b/layout/base/tests/test_zoom_restore_bfcache.html
index 52636d032d7f..d1133a9b044b 100644
--- a/layout/base/tests/test_zoom_restore_bfcache.html
+++ b/layout/base/tests/test_zoom_restore_bfcache.html
@@ -7,123 +7,121 @@
 <script>
 SimpleTest.waitForExplicitFinish();
 
-SimpleTest.enableLegacyUnpartitionedStorage().then(() => {
-  /**
-   * - main page (this one) opens file_zoom_restore_bfcache.html
-   * - file_zoom_restore_bfcache.html sends "handlePageShow" to main page
-   * - main page sends file_zoom_restore_bfcache.html "case1sendData"
-   * - file_zoom_restore_bfcache.html sends "case1data" to main page
-   * - main page sends "case1click" to file_zoom_restore_bfcache.html
-   * - file_zoom_restore_bfcache.html clicks on <a> element, navigating to uri
-   *   file_zoom_restore_bfcache.html?2, and gets bfcached
-   * - file_zoom_restore_bfcache.html?2 sends "handlePageShow" to main page
-   * - main page sends "case2sendData" to file_zoom_restore_bfcache.html?2
-   * - file_zoom_restore_bfcache.html?2 sends "case2data" to main page
-   * - main page sends "case2action" to file_zoom_restore_bfcache.html?2
-   * - file_zoom_restore_bfcache.html?2 sends "case2dataAnimationFrame" to main page
-   * - main page sends "case2back" to file_zoom_restore_bfcache.html?2
-   * - file_zoom_restore_bfcache.html?2 navigates back to file_zoom_restore_bfcache.html
-   * - file_zoom_restore_bfcache.html sends "handlePageShow" to main page
-   * - main page sends "case3sendData to file_zoom_restore_bfcache.html
-   * - file_zoom_restore_bfcache.html sends "case3data" to main page
-   * - main page sends "close to file_zoom_restore_bfcache.html
-   * - file_zoom_restore_bfcache.html closes bc and window and sends back "closed"
-   **/
+/**
+ * - main page (this one) opens file_zoom_restore_bfcache.html
+ * - file_zoom_restore_bfcache.html sends "handlePageShow" to main page
+ * - main page sends file_zoom_restore_bfcache.html "case1sendData"
+ * - file_zoom_restore_bfcache.html sends "case1data" to main page
+ * - main page sends "case1click" to file_zoom_restore_bfcache.html
+ * - file_zoom_restore_bfcache.html clicks on <a> element, navigating to uri
+ *   file_zoom_restore_bfcache.html?2, and gets bfcached
+ * - file_zoom_restore_bfcache.html?2 sends "handlePageShow" to main page
+ * - main page sends "case2sendData" to file_zoom_restore_bfcache.html?2
+ * - file_zoom_restore_bfcache.html?2 sends "case2data" to main page
+ * - main page sends "case2action" to file_zoom_restore_bfcache.html?2
+ * - file_zoom_restore_bfcache.html?2 sends "case2dataAnimationFrame" to main page
+ * - main page sends "case2back" to file_zoom_restore_bfcache.html?2
+ * - file_zoom_restore_bfcache.html?2 navigates back to file_zoom_restore_bfcache.html
+ * - file_zoom_restore_bfcache.html sends "handlePageShow" to main page
+ * - main page sends "case3sendData to file_zoom_restore_bfcache.html
+ * - file_zoom_restore_bfcache.html sends "case3data" to main page
+ * - main page sends "close to file_zoom_restore_bfcache.html
+ * - file_zoom_restore_bfcache.html closes bc and window and sends back "closed"
+ **/
 
-  const originalDPR = window.devicePixelRatio;
-  let loadCount = 0;
-  var bc = new BroadcastChannel("zoomRestoreBfcache");
-  var bcPage2 = new BroadcastChannel("zoomRestoreBfcache?2");
-  bc.onmessage = (msgEvent) => {
-    var msg = msgEvent.data;
-    var command = msg.command;
-    info(`Main page, received command from normal bc=${command}`);
-    switch (command) {
-      case "handlePageShow": {
-        handlePageShow(msgEvent.data.eventPersisted);
-        break;
-      }
-      case "case1data": {
-        is(loadCount, 1, "Case 1");
-        is(msg.devicePixelRatio, originalDPR, "No zoom");
-        bc.postMessage({command: "case1click"});
-        // The end of case 1
-        break;
-      }
-      case "case3data": {
-        is(loadCount, 2, "Case 3");
-        is(msg.devicePixelRatio, originalDPR * 2, "Should preserve zoom when restored");
-        let is_if_ship = SpecialPowers.Services.appinfo.sessionHistoryInParent ? is : todo_is;
-        is_if_ship(msg.frameDevicePixelRatio, originalDPR * 2, "Should preserve zoom on frames too");
-        bc.postMessage({command: "close"});
-        // Now we wait for "closed"
-        break;
-      }
-      case "closed": {
-        is(loadCount, 2, "Case 3");
-        bc.close();
-        SimpleTest.finish();
-        break;
-      }
-      default:
-        ok(false, "should not receive extra messages via BroadcastChannel");
+const originalDPR = window.devicePixelRatio;
+let loadCount = 0;
+var bc = new BroadcastChannel("zoomRestoreBfcache");
+var bcPage2 = new BroadcastChannel("zoomRestoreBfcache?2");
+bc.onmessage = (msgEvent) => {
+  var msg = msgEvent.data;
+  var command = msg.command;
+  info(`Main page, received command from normal bc=${command}`);
+  switch (command) {
+    case "handlePageShow": {
+      handlePageShow(msgEvent.data.eventPersisted);
+      break;
     }
+    case "case1data": {
+      is(loadCount, 1, "Case 1");
+      is(msg.devicePixelRatio, originalDPR, "No zoom");
+      bc.postMessage({command: "case1click"});
+      // The end of case 1
+      break;
+    }
+    case "case3data": {
+      is(loadCount, 2, "Case 3");
+      is(msg.devicePixelRatio, originalDPR * 2, "Should preserve zoom when restored");
+      let is_if_ship = SpecialPowers.Services.appinfo.sessionHistoryInParent ? is : todo_is;
+      is_if_ship(msg.frameDevicePixelRatio, originalDPR * 2, "Should preserve zoom on frames too");
+      bc.postMessage({command: "close"});
+      // Now we wait for "closed"
+      break;
+    }
+    case "closed": {
+      is(loadCount, 2, "Case 3");
+      bc.close();
+      SimpleTest.finish();
+      break;
+    }
+    default:
+      ok(false, "should not receive extra messages via BroadcastChannel");
   }
-  bcPage2.onmessage = (msgEvent) => {
-    var msg = msgEvent.data;
-    var command = msg.command;
-    info(`Main page, received command from bc?2=${command}`);
-    switch (command) {
-      case "handlePageShow": {
-        handlePageShow(msgEvent.data.eventPersisted);
-        break;
-      }
-      case "case2data": {
-        is(loadCount, 2, "Case 2");
-        is(msg.devicePixelRatio, originalDPR, "No zoom (yet)")
-        is(msg.frameDevicePixelRatio, originalDPR, "No zoom on frame either");
-        bcPage2.postMessage({command: "case2action"});
-        // Now we wait for "case2dataAnimationFrame"
-        break;
-      }
-      case "case2dataAnimationFrame": {
-        is(loadCount, 2, "Case 2");
-        is(msg.devicePixelRatio, originalDPR * 2, "Zoomed");
-        is(msg.frameDevicePixelRatio, originalDPR * 2, "Zoomed iframe too");
-        bcPage2.postMessage({command: "case2back"});
-        bcPage2.close();
-        // The end of case 2
-        break;
-      }
-      default:
-        ok(false, "should not receive extra messages via BroadcastChannel");
+}
+bcPage2.onmessage = (msgEvent) => {
+  var msg = msgEvent.data;
+  var command = msg.command;
+  info(`Main page, received command from bc?2=${command}`);
+  switch (command) {
+    case "handlePageShow": {
+      handlePageShow(msgEvent.data.eventPersisted);
+      break;
     }
+    case "case2data": {
+      is(loadCount, 2, "Case 2");
+      is(msg.devicePixelRatio, originalDPR, "No zoom (yet)")
+      is(msg.frameDevicePixelRatio, originalDPR, "No zoom on frame either");
+      bcPage2.postMessage({command: "case2action"});
+      // Now we wait for "case2dataAnimationFrame"
+      break;
+    }
+    case "case2dataAnimationFrame": {
+      is(loadCount, 2, "Case 2");
+      is(msg.devicePixelRatio, originalDPR * 2, "Zoomed");
+      is(msg.frameDevicePixelRatio, originalDPR * 2, "Zoomed iframe too");
+      bcPage2.postMessage({command: "case2back"});
+      bcPage2.close();
+      // The end of case 2
+      break;
+    }
+    default:
+      ok(false, "should not receive extra messages via BroadcastChannel");
   }
-  function handlePageShow(persisted) {
-    ok(typeof persisted == "boolean", "Should get the persisted state from the pageshow event");
-    if (loadCount == 2) {
-      ok(persisted,  "Should've gone into the bfcache after the back navigation");
-    } else {
-      ok(!persisted,  "Should NOT be retrieved from bfcache");
-    }
-
-    if (loadCount == 0) {
-      loadCount++;
-      bc.postMessage({command: "case1sendData"});
-      // Now we wait for the "case1data" message
-    } else if (loadCount == 1) {
-      loadCount++;
-      bcPage2.postMessage({command: "case2sendData"});
-      // Now we wait for the "case2data" message
-    } else {
-      bc.postMessage({command: "case3sendData"});
-      // Now we wait for the "case3data" message
-    }
+}
+function handlePageShow(persisted) {
+  ok(typeof persisted == "boolean", "Should get the persisted state from the pageshow event");
+  if (loadCount == 2) {
+    ok(persisted,  "Should've gone into the bfcache after the back navigation");
+  } else {
+    ok(!persisted,  "Should NOT be retrieved from bfcache");
   }
 
-  // We want to test Gecko's zoom handling, not the front-end's.
-  SpecialPowers.pushPrefEnv({set: [["browser.zoom.siteSpecific", false]]}, () => {
-    window.open('file_zoom_restore_bfcache.html', '_blank', 'noopener');
-  });
+  if (loadCount == 0) {
+    loadCount++;
+    bc.postMessage({command: "case1sendData"});
+    // Now we wait for the "case1data" message
+  } else if (loadCount == 1) {
+    loadCount++;
+    bcPage2.postMessage({command: "case2sendData"});
+    // Now we wait for the "case2data" message
+  } else {
+    bc.postMessage({command: "case3sendData"});
+    // Now we wait for the "case3data" message
+  }
+}
+
+// We want to test Gecko's zoom handling, not the front-end's.
+SpecialPowers.pushPrefEnv({set: [["browser.zoom.siteSpecific", false]]}, () => {
+  window.open('file_zoom_restore_bfcache.html', '_blank', 'noopener');
 });
 </script>
diff --git a/netwerk/cookie/test/mochitest/mochitest.toml b/netwerk/cookie/test/mochitest/mochitest.toml
index d2128e077cd6..f96158f3faea 100644
--- a/netwerk/cookie/test/mochitest/mochitest.toml
+++ b/netwerk/cookie/test/mochitest/mochitest.toml
@@ -8,7 +8,6 @@ support-files = [
 ["test_document_cookie.html"]
 
 ["test_document_cookie_notification.html"]
-scheme = "https"
 
 ["test_fetch.html"]
 
diff --git a/netwerk/cookie/test/mochitest/server_time.sjs b/netwerk/cookie/test/mochitest/server_time.sjs
index 83d80e22903a..58038f7b888e 100644
--- a/netwerk/cookie/test/mochitest/server_time.sjs
+++ b/netwerk/cookie/test/mochitest/server_time.sjs
@@ -5,9 +5,7 @@ function handleRequest(aRequest, aResponse) {
 
   aResponse.setHeader(
     "Set-Cookie",
-    `${
-      parts[0]
-    }=foo; path=/; sameSite=none; secure; partitioned; expires=${new Date(
+    `${parts[0]}=foo; path=/; sameSite=none; secure; expires=${new Date(
       parseInt(parts[2], 10)
     ).toGMTString()}`,
     false
diff --git a/netwerk/cookie/test/mochitest/test_document_cookie_notification.html b/netwerk/cookie/test/mochitest/test_document_cookie_notification.html
index c548a649ba46..b84b6ed045d4 100644
--- a/netwerk/cookie/test/mochitest/test_document_cookie_notification.html
+++ b/netwerk/cookie/test/mochitest/test_document_cookie_notification.html
@@ -24,7 +24,7 @@ Listener.prototype = {
 }
 
 const cl = new Listener();
-document.cookie = "a=" + Math.random() + "; Secure; Partitioned; SameSite=None";
+document.cookie = "a=" + Math.random();
 SimpleTest.waitForExplicitFinish();
 
 </script>
diff --git a/netwerk/test/mochitests/file_testcommon.js b/netwerk/test/mochitests/file_testcommon.js
index 0eca6ec89c2c..4a9b0504e91e 100644
--- a/netwerk/test/mochitests/file_testcommon.js
+++ b/netwerk/test/mochitests/file_testcommon.js
@@ -33,12 +33,6 @@ function setupTest(uri, cookies, loads) {
   gExpectedCookies = cookies;
   gExpectedLoads = loads;
 
-  // If this is an xorigin test, the "oh=hai" cookie set by this frame
-  // in runTest() does not work because we are third-party
-  if (isXOrigin) {
-    gExpectedCookies -= 1;
-  }
-
   // Listen for MessageEvents.
   window.addEventListener("message", messageReceiver);
 
diff --git a/testing/profiles/mochitest/user.js b/testing/profiles/mochitest/user.js
index f87958f8ea01..a4068ac3f611 100644
--- a/testing/profiles/mochitest/user.js
+++ b/testing/profiles/mochitest/user.js
@@ -23,6 +23,11 @@ user_pref("general.smoothScroll", true);
 // storage access API spec for secure contexts.
 user_pref("dom.storage_access.dont_grant_insecure_contexts", false);
 
+// Many mochitests rely upon this behavior (which is being deprecated)
+// while testing other behaviors. We plan to update all tests to not
+// rely upon it, remove this pref, then roll out to release.
+user_pref("privacy.restrict3rdpartystorage.heuristic.window_open", true);
+
 // Turn off update
 user_pref("app.update.disabledForTesting", true);
 
diff --git a/toolkit/components/antitracking/test/browser/browser_permissionInNormalWindows.js b/toolkit/components/antitracking/test/browser/browser_permissionInNormalWindows.js
index beda8f47e4ba..c8b4ac5dcb14 100644
--- a/toolkit/components/antitracking/test/browser/browser_permissionInNormalWindows.js
+++ b/toolkit/components/antitracking/test/browser/browser_permissionInNormalWindows.js
@@ -107,7 +107,6 @@ AntiTracking.runTest(
       "privacy.partition.always_partition_third_party_non_cookie_storage",
       false,
     ],
-    ["privacy.restrict3rdpartystorage.heuristic.window_open", true],
   ], // extra prefs
   true, // run the window.open() test
   true, // run the user interaction test
diff --git a/toolkit/components/antitracking/test/browser/browser_permissionInNormalWindows_alwaysPartition.js b/toolkit/components/antitracking/test/browser/browser_permissionInNormalWindows_alwaysPartition.js
index 6e76518aa1d1..e2eaa6831ab6 100644
--- a/toolkit/components/antitracking/test/browser/browser_permissionInNormalWindows_alwaysPartition.js
+++ b/toolkit/components/antitracking/test/browser/browser_permissionInNormalWindows_alwaysPartition.js
@@ -103,10 +103,7 @@ AntiTracking.runTest(
       );
     });
   },
-  [
-    ["privacy.partition.always_partition_third_party_non_cookie_storage", true],
-    ["privacy.restrict3rdpartystorage.heuristic.window_open", true],
-  ], // extra prefs
+  [["privacy.partition.always_partition_third_party_non_cookie_storage", true]], // extra prefs
   true, // run the window.open() test
   true, // run the user interaction test
   [
diff --git a/toolkit/components/antitracking/test/browser/browser_permissionInPrivateWindows.js b/toolkit/components/antitracking/test/browser/browser_permissionInPrivateWindows.js
index e4daab713904..3786634cc216 100644
--- a/toolkit/components/antitracking/test/browser/browser_permissionInPrivateWindows.js
+++ b/toolkit/components/antitracking/test/browser/browser_permissionInPrivateWindows.js
@@ -45,7 +45,6 @@ AntiTracking.runTest(
       "privacy.partition.always_partition_third_party_non_cookie_storage",
       false,
     ],
-    ["privacy.restrict3rdpartystorage.heuristic.window_open", true],
   ], // extra prefs
   true, // run the window.open() test
   true, // run the user interaction test
diff --git a/toolkit/components/antitracking/test/browser/browser_permissionInPrivateWindows_alwaysPartition.js b/toolkit/components/antitracking/test/browser/browser_permissionInPrivateWindows_alwaysPartition.js
index cef6dab51801..352dbae11d7b 100644
--- a/toolkit/components/antitracking/test/browser/browser_permissionInPrivateWindows_alwaysPartition.js
+++ b/toolkit/components/antitracking/test/browser/browser_permissionInPrivateWindows_alwaysPartition.js
@@ -40,10 +40,7 @@ AntiTracking.runTest(
       );
     });
   },
-  [
-    ["privacy.partition.always_partition_third_party_non_cookie_storage", true],
-    ["privacy.restrict3rdpartystorage.heuristic.window_open", true],
-  ], // extra prefs
+  [["privacy.partition.always_partition_third_party_non_cookie_storage", true]], // extra prefs
   true, // run the window.open() test
   true, // run the user interaction test
   [
diff --git a/toolkit/components/antitracking/test/browser/browser_script.js b/toolkit/components/antitracking/test/browser/browser_script.js
index 02595e97ec62..952e26c1d43b 100644
--- a/toolkit/components/antitracking/test/browser/browser_script.js
+++ b/toolkit/components/antitracking/test/browser/browser_script.js
@@ -19,7 +19,6 @@ add_task(async function () {
         "privacy.restrict3rdpartystorage.userInteractionRequiredForHosts",
         "tracking.example.com,tracking.example.org",
       ],
-      ["privacy.restrict3rdpartystorage.heuristic.window_open", true],
     ],
   });
 
diff --git a/toolkit/components/antitracking/test/browser/browser_storageAccessThirdPartyChecks.js b/toolkit/components/antitracking/test/browser/browser_storageAccessThirdPartyChecks.js
index 9b9a7806f6c8..4793ed9325e8 100644
--- a/toolkit/components/antitracking/test/browser/browser_storageAccessThirdPartyChecks.js
+++ b/toolkit/components/antitracking/test/browser/browser_storageAccessThirdPartyChecks.js
@@ -48,6 +48,7 @@ AntiTracking._createTask({
   errorMessageDomains: [
     "https://tracking.example.org",
     "https://tracking.example.org",
+    "https://tracking.example.org",
   ],
 });
 
diff --git a/toolkit/components/antitracking/test/browser/browser_storageAccessThirdPartyChecks_alwaysPartition.js b/toolkit/components/antitracking/test/browser/browser_storageAccessThirdPartyChecks_alwaysPartition.js
index 3b361b51c84d..8ea97dac686e 100644
--- a/toolkit/components/antitracking/test/browser/browser_storageAccessThirdPartyChecks_alwaysPartition.js
+++ b/toolkit/components/antitracking/test/browser/browser_storageAccessThirdPartyChecks_alwaysPartition.js
@@ -52,6 +52,7 @@ AntiTracking._createTask({
     "https://tracking.example.org",
     "https://tracking.example.org",
     "https://tracking.example.org",
+    "https://tracking.example.org",
     "https://another-tracking.example.net",
     "https://itisatracker.org",
   ],
diff --git a/toolkit/components/antitracking/test/browser/browser_subResources.js b/toolkit/components/antitracking/test/browser/browser_subResources.js
index 1c0bfdec6dfa..1b85aabb243c 100644
--- a/toolkit/components/antitracking/test/browser/browser_subResources.js
+++ b/toolkit/components/antitracking/test/browser/browser_subResources.js
@@ -22,9 +22,6 @@ add_task(async function () {
       ],
       // Bug 1617611: Fix all the tests broken by "cookies SameSite=lax by default"
       ["network.cookie.sameSite.laxByDefault", false],
-      // This test validates old TCP behavior and relies upon the opener heuristic to
-      // give access to cookies to known trackers.
-      ["privacy.restrict3rdpartystorage.heuristic.window_open", true],
     ],
   });
 
diff --git a/toolkit/components/antitracking/test/browser/browser_subResourcesPartitioned.js b/toolkit/components/antitracking/test/browser/browser_subResourcesPartitioned.js
index 5d6a6b6dafbe..c55fad612ff8 100644
--- a/toolkit/components/antitracking/test/browser/browser_subResourcesPartitioned.js
+++ b/toolkit/components/antitracking/test/browser/browser_subResourcesPartitioned.js
@@ -281,9 +281,6 @@ add_task(async function () {
         "privacy.partition.always_partition_third_party_non_cookie_storage",
         false,
       ],
-      // This test validates old TCP behavior and relies upon the opener heuristic to
-      // give access to cookies to known trackers.
-      ["privacy.restrict3rdpartystorage.heuristic.window_open", true],
     ],
   });
 
diff --git a/toolkit/components/antitracking/test/browser/browser_subResourcesPartitioned_alwaysPartition.js b/toolkit/components/antitracking/test/browser/browser_subResourcesPartitioned_alwaysPartition.js
index 4b3c7a2a8129..9e1a57341847 100644
--- a/toolkit/components/antitracking/test/browser/browser_subResourcesPartitioned_alwaysPartition.js
+++ b/toolkit/components/antitracking/test/browser/browser_subResourcesPartitioned_alwaysPartition.js
@@ -286,9 +286,6 @@ add_task(async function () {
         "privacy.partition.always_partition_third_party_non_cookie_storage",
         true,
       ],
-      // This test validates old TCP behavior and relies upon the opener heuristic to
-      // give access to cookies to known trackers.
-      ["privacy.restrict3rdpartystorage.heuristic.window_open", true],
     ],
   });
 
diff --git a/toolkit/components/extensions/test/mochitest/test_ext_subframes_privileges.html b/toolkit/components/extensions/test/mochitest/test_ext_subframes_privileges.html
index 4ce005562481..05862758086d 100644
--- a/toolkit/components/extensions/test/mochitest/test_ext_subframes_privileges.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_subframes_privileges.html
@@ -224,10 +224,6 @@ add_task(async function test_webext_contentscript_iframe_subframe_privileges() {
 });
 
 add_task(async function test_webext_background_remote_subframe_privileges() {
-  // we have to enable unpartitioned cookie access for xorigin tests to set the cookie
-  // where the popup can read it.
-  await SimpleTest.enableLegacyUnpartitionedStorage();
-
   // file_remote_frame.html is opened at the same origin as this test page.
   document.cookie = "cookie=monster";
 
diff --git a/toolkit/components/extensions/test/mochitest/test_ext_webrequest_redirect_bypass_cors.html b/toolkit/components/extensions/test/mochitest/test_ext_webrequest_redirect_bypass_cors.html
index 5dc8a025961a..7ba92f5c80dd 100644
--- a/toolkit/components/extensions/test/mochitest/test_ext_webrequest_redirect_bypass_cors.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_webrequest_redirect_bypass_cors.html
@@ -25,7 +25,9 @@ const WIN_URL =
 
 add_task(async function test_webRequest_redirect_cors_bypass() {
   // disable third-party storage isolation so the test works as expected
-  await SimpleTest.enableLegacyUnpartitionedStorage();
+  await SpecialPowers.pushPrefEnv({
+    set: [["privacy.partition.always_partition_third_party_non_cookie_storage", false]],
+  });
 
   let extension = ExtensionTestUtils.loadExtension({
     manifest: {
diff --git a/toolkit/components/passwordmgr/test/mochitest/test_autofill_from_bfcache.html b/toolkit/components/passwordmgr/test/mochitest/test_autofill_from_bfcache.html
index 7abbc9af8914..d0fcb16e180c 100644
--- a/toolkit/components/passwordmgr/test/mochitest/test_autofill_from_bfcache.html
+++ b/toolkit/components/passwordmgr/test/mochitest/test_autofill_from_bfcache.html
@@ -28,8 +28,6 @@ async function test_crossOriginBfcacheRestore() {
   // If Fission is disabled, the pref is no-op.
   await SpecialPowers.pushPrefEnv({set: [["fission.bfcacheInParent", true]]});
 
-  await SimpleTest.enableLegacyUnpartitionedStorage();
-
   var bc = new BroadcastChannel("form_basic_bfcache");
   window.open("form_basic_bfcache.html", "", "noopener");
   var pageshowCount = 0;
diff --git a/toolkit/components/windowwatcher/test/test_storage_copied.html b/toolkit/components/windowwatcher/test/test_storage_copied.html
index 7a4e63d3c692..de05cd685505 100644
--- a/toolkit/components/windowwatcher/test/test_storage_copied.html
+++ b/toolkit/components/windowwatcher/test/test_storage_copied.html
@@ -24,8 +24,6 @@ same domain as the opener.
     }
 
     add_task(async function() {
-      await SimpleTest.enableLegacyUnpartitionedStorage();
-
       const TEST_VALUE = "test-value";
       // This magic value of 2 means that by default, when content tries
       // to open a new window, it'll actually open in a new window instead