diff --git a/toolkit/components/search/tests/xpcshell/head_search.js b/toolkit/components/search/tests/xpcshell/head_search.js
index a607de834720..3a87c2b11552 100644
--- a/toolkit/components/search/tests/xpcshell/head_search.js
+++ b/toolkit/components/search/tests/xpcshell/head_search.js
@@ -66,15 +66,14 @@ SearchSettings.SETTNGS_INVALIDATION_DELAY = 250;
 
 async function promiseSettingsData() {
   let path = OS.Path.join(OS.Constants.Path.profileDir, SETTINGS_FILENAME);
-  let bytes = await OS.File.read(path, { compression: "lz4" });
-  return JSON.parse(new TextDecoder().decode(bytes));
+  return JSON.parse(await IOUtils.readUTF8(path, { decompress: true }));
 }
 
 function promiseSaveSettingsData(data) {
-  return OS.File.writeAtomic(
+  return IOUtils.write(
     OS.Path.join(OS.Constants.Path.profileDir, SETTINGS_FILENAME),
     new TextEncoder().encode(JSON.stringify(data)),
-    { compression: "lz4" }
+    { compress: true }
   );
 }
 
@@ -197,8 +196,7 @@ async function promiseSetLocale(locale) {
  *   false otherwise.
  */
 async function readJSONFile(file) {
-  let bytes = await OS.File.read(file.path);
-  return JSON.parse(new TextDecoder().decode(bytes));
+  return JSON.parse(await IOUtils.readUTF8(file.path));
 }
 
 /**
diff --git a/toolkit/components/search/tests/xpcshell/searchconfigs/head_searchconfig.js b/toolkit/components/search/tests/xpcshell/searchconfigs/head_searchconfig.js
index 746cbdf4440d..d7b154afd175 100644
--- a/toolkit/components/search/tests/xpcshell/searchconfigs/head_searchconfig.js
+++ b/toolkit/components/search/tests/xpcshell/searchconfigs/head_searchconfig.js
@@ -11,7 +11,6 @@ XPCOMUtils.defineLazyModuleGetters(this, {
   AddonTestUtils: "resource://testing-common/AddonTestUtils.jsm",
   AppConstants: "resource://gre/modules/AppConstants.jsm",
   ObjectUtils: "resource://gre/modules/ObjectUtils.jsm",
-  OS: "resource://gre/modules/osfile.jsm",
   Region: "resource://gre/modules/Region.jsm",
   RemoteSettings: "resource://services-settings/remote-settings.js",
   SearchEngine: "resource://gre/modules/SearchEngine.jsm",
@@ -219,9 +218,7 @@ class SearchConfigTest {
     if (TEST_DEBUG) {
       return ["be", "en-US", "kk", "tr", "ru", "zh-CN", "ach", "unknown"];
     }
-    const data = await OS.File.read(do_get_file("all-locales").path, {
-      encoding: "utf-8",
-    });
+    const data = await IOUtils.readUTF8(do_get_file("all-locales").path);
     // "en-US" is not in all-locales as it is the default locale
     // add it manually to ensure it is tested.
     let locales = [...data.split("\n").filter(e => e != ""), "en-US"];
diff --git a/toolkit/components/search/tests/xpcshell/test_settings_duplicate.js b/toolkit/components/search/tests/xpcshell/test_settings_duplicate.js
index 56ac4abf5cdc..d649bbef235c 100644
--- a/toolkit/components/search/tests/xpcshell/test_settings_duplicate.js
+++ b/toolkit/components/search/tests/xpcshell/test_settings_duplicate.js
@@ -97,10 +97,10 @@ add_task(async function setup() {
   enginesSettings.buildID = appInfo.platformBuildID;
   enginesSettings.appVersion = appInfo.version;
 
-  await OS.File.writeAtomic(
+  await IOUtils.write(
     OS.Path.join(OS.Constants.Path.profileDir, SETTINGS_FILENAME),
     new TextEncoder().encode(JSON.stringify(enginesSettings)),
-    { compression: "lz4" }
+    { compress: true }
   );
 });
 
diff --git a/toolkit/components/search/tests/xpcshell/test_webextensions_startup_remove.js b/toolkit/components/search/tests/xpcshell/test_webextensions_startup_remove.js
index 4e5de5644950..07ebabc42f2e 100644
--- a/toolkit/components/search/tests/xpcshell/test_webextensions_startup_remove.js
+++ b/toolkit/components/search/tests/xpcshell/test_webextensions_startup_remove.js
@@ -51,7 +51,7 @@ add_task(async function test_removeAddonOnStartup() {
   // Now remove it, reset the search service and start up the add-on manager.
   // Note: the saved settings will have the engine in. If this didn't work,
   // the engine would still be present.
-  await OS.File.remove(
+  await IOUtils.remove(
     OS.Path.join(profile.path, "extensions", `${ENGINE_ID}.xpi`)
   );