diff --git a/make.js b/make.js
index 8392bdce9..a234017e1 100644
--- a/make.js
+++ b/make.js
@@ -630,6 +630,7 @@ target.firefox = function() {
     defines: defines,
     copy: [
       [COMMON_WEB_FILES, FIREFOX_BUILD_CONTENT_DIR + '/web'],
+      ['web/compatibility.js', FIREFOX_BUILD_CONTENT_DIR + '/web'],
       ['external/bcmaps/*', FIREFOX_BUILD_CONTENT_DIR + '/web/cmaps'],
       [FIREFOX_EXTENSION_DIR + 'tools/l10n.js',
        FIREFOX_BUILD_CONTENT_DIR + '/web']
diff --git a/web/viewer.html b/web/viewer.html
index 00b303f9d..42911b05f 100644
--- a/web/viewer.html
+++ b/web/viewer.html
@@ -38,7 +38,7 @@ http://sourceforge.net/adobe/cmap/wiki/License/
     <link rel="resource" type="application/l10n" href="locale/locale.properties"/>
 <!--#endif-->
 
-<!--#if !(FIREFOX || MOZCENTRAL || CHROME || MINIFIED)-->
+<!--#if !(MOZCENTRAL || CHROME || MINIFIED)-->
     <script src="compatibility.js"></script>
 <!--#endif-->