Bug 1747461 - Remove FileUtils.getFile from browser/base r=mossop

Differential Revision: https://phabricator.services.mozilla.com/D134896

browser/base/content/test/favicons/browser_favicon_nostore.js

@@ -116,9 +116,17 @@ add_task(async function root_icon_stored() {
   });
   server.registerFile(
     "/favicon.ico",
-    FileUtils.getFile(
+    new FileUtils.File(
-      "CurWorkD",
+      PathUtils.join(
-      `/browser/browser/base/content/test/favicons/no-store.png`.split("/")
+        Services.dirsvc.get("CurWorkD", Ci.nsIFile).path,
+        "browser",
+        "browser",
+        "base",
+        "content",
+        "test",
+        "favicons",
+        "no-store.png"
+      )
     )
   );
   server.registerPathHandler("/page", (request, response) => {