diff --git a/toolkit/mozapps/extensions/test/xpcshell/test_system_upgrades.js b/toolkit/mozapps/extensions/test/xpcshell/test_system_upgrades.js
index c1f565b6e1f3..e68341b8df67 100644
--- a/toolkit/mozapps/extensions/test/xpcshell/test_system_upgrades.js
+++ b/toolkit/mozapps/extensions/test/xpcshell/test_system_upgrades.js
@@ -351,7 +351,7 @@ add_task(async function test_system_addon_precedence() {
   await AddonTestUtils.promiseShutdownManager();
   await AddonTestUtils.overrideBuiltIns(builtInOverride);
   await promiseInstallDefaultSystemAddon(ADDON_ID, "1.5");
-  await AddonTestUtils.promiseStartupManager(2);
+  await AddonTestUtils.promiseStartupManager("2");
   await checkAddon(
     "1.5",
     BOOTSTRAP_REASONS.ADDON_DOWNGRADE,
diff --git a/toolkit/mozapps/extensions/test/xpcshell/test_webextension_theme.js b/toolkit/mozapps/extensions/test/xpcshell/test_webextension_theme.js
index 20d4f01bfa95..897404a8b406 100644
--- a/toolkit/mozapps/extensions/test/xpcshell/test_webextension_theme.js
+++ b/toolkit/mozapps/extensions/test/xpcshell/test_webextension_theme.js
@@ -294,7 +294,7 @@ add_task(async function test_theme_update() {
   let addon = await AddonManager.getAddonByID(DEFAULT_THEME);
   ok(!addon.userDisabled, "default theme is enabled");
 
-  await AddonTestUtils.promiseRestartManager(2);
+  await AddonTestUtils.promiseRestartManager("2");
 
   addon = await AddonManager.getAddonByID(DEFAULT_THEME);
   ok(!addon.userDisabled, "default theme is enabled after upgrade");