--- a/toolkit/mozapps/extensions/test/browser/browser_globalwarnings.js
+++ b/toolkit/mozapps/extensions/test/browser/browser_globalwarnings.js
@@ -88,17 +88,19 @@ add_task(async function checkCompatibili
   await extension.unload();
 });
 
 add_task(async function checkSecurity() {
   info("Testing update security checking warning");
 
   var pref = "extensions.checkUpdateSecurity";
   info("Setting " + pref + " pref to false");
-  Services.prefs.setBoolPref(pref, false);
+  await SpecialPowers.pushPrefEnv({
+    set: [[pref, false]],
+  });
 
   let id = "test-security@mochi.test";
   let extension = ExtensionTestUtils.loadExtension({
     manifest: { applications: { gecko: { id } } },
     useAddonManager: "temporary",
   });
   await extension.startup();
 

--- a/toolkit/mozapps/extensions/test/browser/browser_history_navigation.js
+++ b/toolkit/mozapps/extensions/test/browser/browser_history_navigation.js
@@ -16,20 +16,16 @@ const { AddonTestUtils } = ChromeUtils.i
   "resource://testing-common/AddonTestUtils.jsm"
 );
 
 AddonTestUtils.initMochitest(this);
 
 const MAIN_URL = `https://example.com/${RELATIVE_DIR}discovery.html`;
 const DISCOAPI_URL = `http://example.com/${RELATIVE_DIR}/discovery/api_response_empty.json`;
 
-// Clearing this pref is currently done from a cleanup function registered
-// by the head.js file.
-Services.prefs.setCharPref(PREF_DISCOVERURL, MAIN_URL);
-
 var gProvider = new MockProvider();
 gProvider.createAddons([
   {
     id: "test1@tests.mozilla.org",
     name: "Test add-on 1",
     description: "foo",
   },
   {

--- a/toolkit/mozapps/extensions/test/browser/browser_installssl.js
+++ b/toolkit/mozapps/extensions/test/browser/browser_installssl.js
@@ -31,20 +31,16 @@ function test() {
     var cos = Cc["@mozilla.org/security/certoverride;1"].getService(
       Ci.nsICertOverrideService
     );
     cos.clearValidityOverride("nocert.example.com", -1);
     cos.clearValidityOverride("self-signed.example.com", -1);
     cos.clearValidityOverride("untrusted.example.com", -1);
     cos.clearValidityOverride("expired.example.com", -1);
 
-    try {
-      Services.prefs.clearUserPref(PREF_INSTALL_REQUIREBUILTINCERTS);
-    } catch (e) {}
-
     if (gPendingInstall) {
       gTests = [];
       ok(
         false,
         "Timed out in the middle of downloading " +
           gPendingInstall.sourceURI.spec
       );
       try {
@@ -172,18 +168,20 @@ add_test(function() {
   add_install_test(EXPIRED, UNTRUSTED, NETWORK_FAILURE);
   add_install_test(EXPIRED, EXPIRED, NETWORK_FAILURE);
 
   run_install_tests(run_next_test);
 });
 
 // Runs tests without requiring built-in certificates, no certificate
 // exceptions and no hashes
-add_test(function() {
-  Services.prefs.setBoolPref(PREF_INSTALL_REQUIREBUILTINCERTS, false);
+add_test(async function() {
+  await SpecialPowers.pushPrefEnv({
+    set: [[PREF_INSTALL_REQUIREBUILTINCERTS, false]],
+  });
 
   // Tests that a simple install works as expected.
   add_install_test(HTTP, null, SUCCESS);
   add_install_test(HTTPS, null, SUCCESS);
   add_install_test(NOCERT, null, NETWORK_FAILURE);
   add_install_test(SELFSIGNED, null, NETWORK_FAILURE);
   add_install_test(UNTRUSTED, null, NETWORK_FAILURE);
   add_install_test(EXPIRED, null, NETWORK_FAILURE);
@@ -241,18 +239,20 @@ add_test(function() {
 
 // Set up overrides for the next test.
 add_test(() => {
   addCertOverrides().then(run_next_test);
 });
 
 // Runs tests with built-in certificates required, all certificate exceptions
 // and no hashes
-add_test(function() {
-  Services.prefs.clearUserPref(PREF_INSTALL_REQUIREBUILTINCERTS);
+add_test(async function() {
+  await SpecialPowers.pushPrefEnv({
+    clear: [[PREF_INSTALL_REQUIREBUILTINCERTS]],
+  });
 
   // Tests that a simple install works as expected.
   add_install_test(HTTP, null, SUCCESS);
   add_install_test(HTTPS, null, NETWORK_FAILURE);
   add_install_test(NOCERT, null, NETWORK_FAILURE);
   add_install_test(SELFSIGNED, null, NETWORK_FAILURE);
   add_install_test(UNTRUSTED, null, NETWORK_FAILURE);
   add_install_test(EXPIRED, null, NETWORK_FAILURE);
@@ -305,18 +305,20 @@ add_test(function() {
   add_install_test(EXPIRED, UNTRUSTED, NETWORK_FAILURE);
   add_install_test(EXPIRED, EXPIRED, NETWORK_FAILURE);
 
   run_install_tests(run_next_test);
 });
 
 // Runs tests without requiring built-in certificates, all certificate
 // exceptions and no hashes
-add_test(function() {
-  Services.prefs.setBoolPref(PREF_INSTALL_REQUIREBUILTINCERTS, false);
+add_test(async function() {
+  await SpecialPowers.pushPrefEnv({
+    set: [[PREF_INSTALL_REQUIREBUILTINCERTS, false]],
+  });
 
   // Tests that a simple install works as expected.
   add_install_test(HTTP, null, SUCCESS);
   add_install_test(HTTPS, null, SUCCESS);
   add_install_test(NOCERT, null, SUCCESS);
   add_install_test(SELFSIGNED, null, SUCCESS);
   add_install_test(UNTRUSTED, null, SUCCESS);
   add_install_test(EXPIRED, null, SUCCESS);

--- a/toolkit/mozapps/extensions/test/browser/browser_updatessl.js
+++ b/toolkit/mozapps/extensions/test/browser/browser_updatessl.js
@@ -63,18 +63,16 @@ function test() {
   registerCleanupFunction(function() {
     observerService.removeObserver(HTTPObserver);
   });
 
   run_next_test();
 }
 
 function end_test() {
-  Services.prefs.clearUserPref(PREF_UPDATE_REQUIREBUILTINCERTS);
-
   var cos = Cc["@mozilla.org/security/certoverride;1"].getService(
     Ci.nsICertOverrideService
   );
   cos.clearValidityOverride("nocert.example.com", -1);
   cos.clearValidityOverride("self-signed.example.com", -1);
   cos.clearValidityOverride("untrusted.example.com", -1);
   cos.clearValidityOverride("expired.example.com", -1);
 
@@ -185,18 +183,20 @@ add_test(function() {
   add_update_test(EXPIRED, UNTRUSTED, DOWNLOAD_ERROR);
   add_update_test(EXPIRED, EXPIRED, DOWNLOAD_ERROR);
 
   run_update_tests(run_next_test);
 });
 
 // Runs tests without requiring built-in certificates and no certificate
 // exceptions.
-add_test(function() {
-  Services.prefs.setBoolPref(PREF_UPDATE_REQUIREBUILTINCERTS, false);
+add_test(async function() {
+  await SpecialPowers.pushPrefEnv({
+    set: [[PREF_UPDATE_REQUIREBUILTINCERTS, false]],
+  });
 
   // Tests that a simple update.json retrieval works as expected.
   add_update_test(HTTP, null, SUCCESS);
   add_update_test(HTTPS, null, SUCCESS);
   add_update_test(NOCERT, null, DOWNLOAD_ERROR);
   add_update_test(SELFSIGNED, null, DOWNLOAD_ERROR);
   add_update_test(UNTRUSTED, null, DOWNLOAD_ERROR);
   add_update_test(EXPIRED, null, DOWNLOAD_ERROR);
@@ -253,18 +253,20 @@ add_test(function() {
 });
 
 // Set up overrides for the next test.
 add_test(() => {
   addCertOverrides().then(run_next_test);
 });
 
 // Runs tests with built-in certificates required and all certificate exceptions.
-add_test(function() {
-  Services.prefs.clearUserPref(PREF_UPDATE_REQUIREBUILTINCERTS);
+add_test(async function() {
+  await SpecialPowers.pushPrefEnv({
+    clear: [[PREF_UPDATE_REQUIREBUILTINCERTS]],
+  });
 
   // Tests that a simple update.json retrieval works as expected.
   add_update_test(HTTP, null, SUCCESS);
   add_update_test(HTTPS, null, DOWNLOAD_ERROR);
   add_update_test(NOCERT, null, DOWNLOAD_ERROR);
   add_update_test(SELFSIGNED, null, DOWNLOAD_ERROR);
   add_update_test(UNTRUSTED, null, DOWNLOAD_ERROR);
   add_update_test(EXPIRED, null, DOWNLOAD_ERROR);
@@ -317,18 +319,20 @@ add_test(function() {
   add_update_test(EXPIRED, UNTRUSTED, DOWNLOAD_ERROR);
   add_update_test(EXPIRED, EXPIRED, DOWNLOAD_ERROR);
 
   run_update_tests(run_next_test);
 });
 
 // Runs tests without requiring built-in certificates and all certificate
 // exceptions.
-add_test(function() {
-  Services.prefs.setBoolPref(PREF_UPDATE_REQUIREBUILTINCERTS, false);
+add_test(async function() {
+  await SpecialPowers.pushPrefEnv({
+    set: [[PREF_UPDATE_REQUIREBUILTINCERTS, false]],
+  });
 
   // Tests that a simple update.json retrieval works as expected.
   add_update_test(HTTP, null, SUCCESS);
   add_update_test(HTTPS, null, SUCCESS);
   add_update_test(NOCERT, null, SUCCESS);
   add_update_test(SELFSIGNED, null, SUCCESS);
   add_update_test(UNTRUSTED, null, SUCCESS);
   add_update_test(EXPIRED, null, SUCCESS);

--- a/toolkit/mozapps/extensions/test/browser/browser_webapi.js
+++ b/toolkit/mozapps/extensions/test/browser/browser_webapi.js
@@ -1,17 +1,18 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/
  */
 
 const TESTPAGE = `${SECURE_TESTROOT}webapi_checkavailable.html`;
 
-Services.prefs.setBoolPref("extensions.webapi.testing", true);
-registerCleanupFunction(() => {
-  Services.prefs.clearUserPref("extensions.webapi.testing");
+add_task(async function setup() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["extensions.webapi.testing", true]],
+  });
 });
 
 function testWithAPI(task) {
   return async function() {
     await BrowserTestUtils.withNewTab(TESTPAGE, task);
   };
 }
 

--- a/toolkit/mozapps/extensions/test/browser/browser_webapi_access.js
+++ b/toolkit/mozapps/extensions/test/browser/browser_webapi_access.js
@@ -1,16 +1,12 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/
  */
 
-registerCleanupFunction(() => {
-  Services.prefs.clearUserPref("extensions.webapi.testing");
-});
-
 function check_frame_availability(browser) {
   return check_availability(browser.browsingContext.children[0]);
 }
 
 function check_availability(browser) {
   return SpecialPowers.spawn(browser, [], async function() {
     return content.document.getElementById("result").textContent == "true";
   });
@@ -24,17 +20,19 @@ add_task(async function test_not_availab
       let available = await check_availability(browser);
       ok(!available, "API should not be available.");
     }
   );
 });
 
 // Test that with testing on the API is available in the test domain
 add_task(async function test_available() {
-  Services.prefs.setBoolPref("extensions.webapi.testing", true);
+  await SpecialPowers.pushPrefEnv({
+    set: [["extensions.webapi.testing", true]],
+  });
 
   await BrowserTestUtils.withNewTab(
     `${SECURE_TESTROOT}webapi_checkavailable.html`,
     async function test_not_available(browser) {
       let available = await check_availability(browser);
       ok(available, "API should be available.");
     }
   );

--- a/toolkit/mozapps/extensions/test/browser/browser_webapi_addon_listener.js
+++ b/toolkit/mozapps/extensions/test/browser/browser_webapi_addon_listener.js
@@ -1,13 +1,14 @@
 const TESTPAGE = `${SECURE_TESTROOT}webapi_addon_listener.html`;
 
-Services.prefs.setBoolPref("extensions.webapi.testing", true);
-registerCleanupFunction(() => {
-  Services.prefs.clearUserPref("extensions.webapi.testing");
+add_task(async function setup() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["extensions.webapi.testing", true]],
+  });
 });
 
 async function getListenerEvents(browser) {
   let result = await SpecialPowers.spawn(browser, [], async function() {
     return content.document.getElementById("result").textContent;
   });
 
   return result.split("\n").map(JSON.parse);

--- a/toolkit/mozapps/extensions/test/browser/browser_webapi_enable.js
+++ b/toolkit/mozapps/extensions/test/browser/browser_webapi_enable.js
@@ -1,13 +1,14 @@
 const TESTPAGE = `${SECURE_TESTROOT}webapi_addon_listener.html`;
 
-Services.prefs.setBoolPref("extensions.webapi.testing", true);
-registerCleanupFunction(() => {
-  Services.prefs.clearUserPref("extensions.webapi.testing");
+add_task(async function setup() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["extensions.webapi.testing", true]],
+  });
 });
 
 async function getListenerEvents(browser) {
   let result = await SpecialPowers.spawn(browser, [], async function() {
     return content.document.getElementById("result").textContent;
   });
 
   return result.split("\n").map(JSON.parse);

--- a/toolkit/mozapps/extensions/test/browser/browser_webapi_uninstall.js
+++ b/toolkit/mozapps/extensions/test/browser/browser_webapi_uninstall.js
@@ -1,17 +1,18 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/
  */
 
 const TESTPAGE = `${SECURE_TESTROOT}webapi_checkavailable.html`;
 
-Services.prefs.setBoolPref("extensions.webapi.testing", true);
-registerCleanupFunction(() => {
-  Services.prefs.clearUserPref("extensions.webapi.testing");
+add_task(async function setup() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["extensions.webapi.testing", true]],
+  });
 });
 
 function testWithAPI(task) {
   return async function() {
     await BrowserTestUtils.withNewTab(TESTPAGE, task);
   };
 }
 

--- a/toolkit/mozapps/extensions/test/browser/browser_webext_incognito.js
+++ b/toolkit/mozapps/extensions/test/browser/browser_webext_incognito.js
@@ -279,18 +279,16 @@ add_task(async function test_badge_and_t
         "action",
         "aboutAddons",
         "off",
         { ...expectedExtras, addonId: "@test-override-permanent" },
       ],
     ],
     { methods: ["action"] }
   );
-
-  Services.prefs.clearUserPref("extensions.allowPrivateBrowsingByDefault");
 });
 
 add_task(async function test_addon_preferences_button() {
   await SpecialPowers.pushPrefEnv({
     set: [["extensions.allowPrivateBrowsingByDefault", false]],
   });
 
   let addons = new Map([