diff --git a/browser/components/downloads/test/browser/head.js b/browser/components/downloads/test/browser/head.js
index 727fcb39092e..a184bd1582d7 100644
--- a/browser/components/downloads/test/browser/head.js
+++ b/browser/components/downloads/test/browser/head.js
@@ -169,26 +169,23 @@ async function task_openPanel() {
 }
 
 async function setDownloadDir() {
-  let tmpDir = Services.dirsvc.get("TmpD", Ci.nsIFile);
-  tmpDir.append("testsavedir");
-  if (!tmpDir.exists()) {
-    tmpDir.create(Ci.nsIFile.DIRECTORY_TYPE, 0o755);
-    registerCleanupFunction(function() {
-      try {
-        tmpDir.remove(true);
-      } catch (e) {
-        // On Windows debug build this may fail.
-      }
-    });
-  }
-
-  await SpecialPowers.pushPrefEnv({
-    set: [
-      ["browser.download.folderList", 2],
-      ["browser.download.dir", tmpDir.path],
-    ],
+  let tmpDir = await PathUtils.getTempDir();
+  tmpDir = PathUtils.join(
+    tmpDir,
+    "testsavedir" + Math.floor(Math.random() * 2 ** 32)
+  );
+  // Create this dir if it doesn't exist (ignores existing dirs)
+  await IOUtils.makeDirectory(tmpDir);
+  registerCleanupFunction(async function() {
+    try {
+      await IOUtils.remove(tmpDir, { recursive: true });
+    } catch (e) {
+      Cu.reportError(e);
+    }
   });
-  return tmpDir.path;
+  Services.prefs.setIntPref("browser.download.folderList", 2);
+  Services.prefs.setCharPref("browser.download.dir", tmpDir);
+  return tmpDir;
 }
 
 let gHttpServer = null;
diff --git a/browser/components/downloads/test/unit/head.js b/browser/components/downloads/test/unit/head.js
index 6e26b8194526..6769bfe79ab5 100644
--- a/browser/components/downloads/test/unit/head.js
+++ b/browser/components/downloads/test/unit/head.js
@@ -56,21 +56,23 @@ async function createDownloadedFile(pathname, contents) {
 let gDownloadDir;
 
 async function setDownloadDir() {
-  let tmpDir = Services.dirsvc.get("TmpD", Ci.nsIFile);
-  tmpDir.append("testsavedir");
-  if (!tmpDir.exists()) {
-    tmpDir.create(Ci.nsIFile.DIRECTORY_TYPE, 0o755);
-    registerCleanupFunction(function() {
-      try {
-        tmpDir.remove(true);
-      } catch (e) {
-        // On Windows debug build this may fail.
-      }
-    });
-  }
+  let tmpDir = Services.dirsvc.get("TmpD", Ci.nsIFile).path;
+  tmpDir = PathUtils.join(
+    tmpDir,
+    "testsavedir" + Math.floor(Math.random() * 2 ** 32)
+  );
+  // Create this dir if it doesn't exist (ignores existing dirs)
+  await IOUtils.makeDirectory(tmpDir);
+  registerCleanupFunction(async function() {
+    try {
+      await IOUtils.remove(tmpDir, { recursive: true });
+    } catch (e) {
+      Cu.reportError(e);
+    }
+  });
   Services.prefs.setIntPref("browser.download.folderList", 2);
-  Services.prefs.setCharPref("browser.download.dir", tmpDir.path);
-  return tmpDir.path;
+  Services.prefs.setCharPref("browser.download.dir", tmpDir);
+  return tmpDir;
 }
 
 /**
diff --git a/uriloader/exthandler/tests/mochitest/head.js b/uriloader/exthandler/tests/mochitest/head.js
index bffd0dc20aae..066dd7beb26b 100644
--- a/uriloader/exthandler/tests/mochitest/head.js
+++ b/uriloader/exthandler/tests/mochitest/head.js
@@ -248,3 +248,30 @@ function setupMailHandler() {
     gHandlerSvc.store(mailHandlerInfo);
   });
 }
+
+let gDownloadDir;
+
+async function setDownloadDir() {
+  let tmpDir = await PathUtils.getTempDir();
+  tmpDir = PathUtils.join(
+    tmpDir,
+    "testsavedir" + Math.floor(Math.random() * 2 ** 32)
+  );
+  // Create this dir if it doesn't exist (ignores existing dirs)
+  await IOUtils.makeDirectory(tmpDir);
+  registerCleanupFunction(async function() {
+    try {
+      await IOUtils.remove(tmpDir, { recursive: true });
+    } catch (e) {
+      Cu.reportError(e);
+    }
+  });
+  Services.prefs.setIntPref("browser.download.folderList", 2);
+  Services.prefs.setCharPref("browser.download.dir", tmpDir);
+  return tmpDir;
+}
+
+add_task(async function test_common_initialize() {
+  gDownloadDir = await setDownloadDir();
+  Services.prefs.setCharPref("browser.download.loglevel", "Debug");
+});