diff --git a/testing/xpcshell/head.js b/testing/xpcshell/head.js
index 5cc705d06835..3f347c776f14 100644
--- a/testing/xpcshell/head.js
+++ b/testing/xpcshell/head.js
@@ -12,7 +12,7 @@
 
 /* defined by the harness */
 /* globals _HEAD_FILES, _HEAD_JS_PATH, _JSDEBUGGER_PORT, _JSCOV_DIR,
-    _MOZINFO_JS_PATH, _TEST_FILE, _TEST_NAME, _TESTING_MODULES_DIR:true,
+    _MOZINFO_JS_PATH, _TEST_FILE, _TEST_NAME, _TEST_CWD, _TESTING_MODULES_DIR:true,
     _PREFS_FILE */
 
 /* defined by XPCShellImpl.cpp */
@@ -64,6 +64,8 @@ let _XPCOMUtils = ChromeUtils.import(
   null
 ).XPCOMUtils;
 
+let _OS = ChromeUtils.import("resource://gre/modules/osfile.jsm", null).OS;
+
 // Support a common assertion library, Assert.jsm.
 var AssertCls = ChromeUtils.import("resource://testing-common/Assert.jsm", null)
   .Assert;
@@ -503,6 +505,20 @@ function _initDebugging(port) {
 }
 
 function _execute_test() {
+  if (typeof _TEST_CWD != "undefined") {
+    let cwd_complete = false;
+    _OS.File.setCurrentDirectory(_TEST_CWD)
+      .then(_ => (cwd_complete = true))
+      .catch(e => {
+        _testLogger.error(_exception_message(e));
+        cwd_complete = true;
+      });
+    _Services.tm.spinEventLoopUntil(
+      "Test(xpcshell/head.js:setCurrentDirectory)",
+      () => cwd_complete
+    );
+  }
+
   if (runningInParent && _AppConstants.platform == "android") {
     _Services.obs.notifyObservers(null, "profile-after-change");
     // Wake up GeckoViewStartup
@@ -651,7 +667,7 @@ function _execute_test() {
     .catch(reportCleanupError)
     .then(() => (complete = true));
   _Services.tm.spinEventLoopUntil(
-    "Test(xpcshel/head.js:_execute_test)",
+    "Test(xpcshell/head.js:_execute_test)",
     () => complete
   );
   if (cleanupStartTime) {
@@ -1368,6 +1384,10 @@ function do_load_child_test_harness() {
     command += " const _JSCOV_DIR=" + uneval(_JSCOV_DIR) + ";";
   }
 
+  if (typeof _TEST_CWD != "undefined") {
+    command += " const _TEST_CWD=" + uneval(_TEST_CWD) + ";";
+  }
+
   if (_TESTING_MODULES_DIR) {
     command +=
       " const _TESTING_MODULES_DIR=" + uneval(_TESTING_MODULES_DIR) + ";";