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 405374f6886da4..bb8eaf6b87c451 100644
--- a/gulpfile.mjs
+++ b/gulpfile.mjs
@@ -46,7 +46,6 @@ 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/";
@@ -1262,25 +1261,29 @@ 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";
+  const MODIFICATION_WARNING = `
+//
+// THIS FILE IS GENERATED AUTOMATICALLY, DO NOT EDIT MANUALLY!
+//
+`;
 
-  const bundleDefines = builder.merge(DEFINES, {
-    DEFAULT_PREFERENCES: getDefaultPreferences("mozcentral/"),
-  });
+  const prefs = getDefaultPreferences("mozcentral/");
+  const buf = [licenseHeader, MODIFICATION_WARNING];
 
-  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});`);
+  }
+
+  return createStringSource(fileName, buf.join("\n"));
 }
 
 function replaceMozcentralCSS() {
@@ -1308,8 +1311,7 @@ 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,
@@ -1382,10 +1384,7 @@ gulp.task(
           .src("l10n/en-US/*.properties")
           .pipe(gulp.dest(MOZCENTRAL_L10N_DIR)),
         gulp.src("LICENSE").pipe(gulp.dest(MOZCENTRAL_EXTENSION_DIR)),
-        gulp
-          .src(FIREFOX_CONTENT_DIR + "PdfJsDefaultPreferences.sys.mjs")
-          .pipe(transform("utf8", preprocessDefaultPreferences))
-          .pipe(gulp.dest(MOZCENTRAL_CONTENT_DIR)),
+        createDefaultPrefsFile().pipe(gulp.dest(MOZCENTRAL_CONTENT_DIR)),
       ]);
     }
   )