diff --git a/extensions/firefox/.eslintrc b/extensions/firefox/.eslintrc
deleted file mode 100644
index e5ae68046fee78..00000000000000
--- a/extensions/firefox/.eslintrc
+++ /dev/null
@@ -1,22 +0,0 @@
-{
-  // Note: The root .eslintrc file will define the base rules,
-  // but mozilla/recommended will override them for the rules it sets. Finally,
-  // the rules in this file will take precedence.
-  "extends": [
-    "plugin:mozilla/recommended",
-  ],
-
-  "plugins": [
-    "mozilla"
-  ],
-
-  "rules": {
-    // Other rules mozilla/recommended hasn't enabled yet.
-    "no-shadow": "error",
-    "arrow-body-style": ["error", "as-needed"],
-    "arrow-parens": ["error", "always"],
-    "constructor-super": "error",
-    "no-confusing-arrow": "error",
-    "no-useless-constructor": "error",
-  },
-}
diff --git a/extensions/firefox/content/PdfJsDefaultPreferences.sys.mjs b/extensions/firefox/content/PdfJsDefaultPreferences.sys.mjs
deleted file mode 100644
index 738adad80b6da3..00000000000000
--- a/extensions/firefox/content/PdfJsDefaultPreferences.sys.mjs
+++ /dev/null
@@ -1,18 +0,0 @@
-/* Copyright 2018 Mozilla Foundation
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-export const PdfJsDefaultPreferences = Object.freeze(
-  PDFJSDev.eval("DEFAULT_PREFERENCES")
-);
diff --git a/gulpfile.mjs b/gulpfile.mjs
index 58fc0240493977..a1c484bddd1609 100644
--- a/gulpfile.mjs
+++ b/gulpfile.mjs
@@ -53,7 +53,6 @@ const __dirname = path.dirname(fileURLToPath(import.meta.url));
 const BUILD_DIR = "build/";
 const L10N_DIR = "l10n/";
 const TEST_DIR = "test/";
-const EXTENSION_SRC_DIR = "extensions/";
 
 const BASELINE_DIR = BUILD_DIR + "baseline/";
 const MOZCENTRAL_BASELINE_DIR = BUILD_DIR + "mozcentral.baseline/";
@@ -1278,26 +1277,28 @@ gulp.task(
   )
 );
 
-function preprocessDefaultPreferences(content) {
+function createDefaultPrefsFile() {
+  const fileName = "PdfJsViewerPrefs.js";
   const licenseHeader = fs.readFileSync("./src/license_header.js").toString();
 
   const MODIFICATION_WARNING =
-    "//\n// THIS FILE IS GENERATED AUTOMATICALLY, DO NOT EDIT MANUALLY!\n//\n";
+    "// THIS FILE IS GENERATED AUTOMATICALLY, DO NOT EDIT MANUALLY!\n";
 
-  const bundleDefines = {
-    ...DEFINES,
-    DEFAULT_PREFERENCES: getDefaultPreferences("mozcentral/"),
-  };
+  const prefs = getDefaultPreferences("mozcentral/");
+  const buf = [];
 
-  content = preprocessPDFJSCode(
-    {
-      rootPath: __dirname,
-      defines: bundleDefines,
-    },
-    content
-  );
+  for (const name in prefs) {
+    let value = prefs[name];
 
-  return licenseHeader + "\n" + MODIFICATION_WARNING + "\n" + content + "\n";
+    if (typeof value === "string") {
+      value = `"${value}"`;
+    }
+    buf.push(`pref("pdfjs.${name}", ${value});`);
+  }
+  buf.sort();
+  buf.unshift(licenseHeader, MODIFICATION_WARNING);
+
+  return createStringSource(fileName, buf.join("\n"));
 }
 
 function replaceMozcentralCSS() {
@@ -1325,8 +1326,7 @@ gulp.task(
         MOZCENTRAL_EXTENSION_DIR = MOZCENTRAL_DIR + "browser/extensions/pdfjs/",
         MOZCENTRAL_CONTENT_DIR = MOZCENTRAL_EXTENSION_DIR + "content/",
         MOZCENTRAL_L10N_DIR =
-          MOZCENTRAL_DIR + "browser/locales/en-US/pdfviewer/",
-        FIREFOX_CONTENT_DIR = EXTENSION_SRC_DIR + "/firefox/content/";
+          MOZCENTRAL_DIR + "browser/locales/en-US/pdfviewer/";
 
       const MOZCENTRAL_WEB_FILES = [
         ...COMMON_WEB_FILES,
@@ -1401,12 +1401,7 @@ gulp.task(
         gulp
           .src("LICENSE", { encoding: false })
           .pipe(gulp.dest(MOZCENTRAL_EXTENSION_DIR)),
-        gulp
-          .src(FIREFOX_CONTENT_DIR + "PdfJsDefaultPreferences.sys.mjs", {
-            encoding: false,
-          })
-          .pipe(transform("utf8", preprocessDefaultPreferences))
-          .pipe(gulp.dest(MOZCENTRAL_CONTENT_DIR)),
+        createDefaultPrefsFile().pipe(gulp.dest(MOZCENTRAL_CONTENT_DIR)),
       ]);
     }
   )