--- a/python/mozbuild/mozpack/packager/formats.py
+++ b/python/mozbuild/mozpack/packager/formats.py
@@ -331,14 +331,15 @@ class OmniJarSubFormatter(PiecemealForma
             return len(path) == 1 or \
                 (path[1] != 'cursors' and path[1] != 'MainMenu.nib')
         if path[0] == 'defaults':
             return len(path) != 3 or \
                 not (path[2] == 'channel-prefs.js' and
                      path[1] in ['pref', 'preferences'])
         return path[0] in [
             'modules',
+            'dictionaries',
             'greprefs.js',
             'hyphenation',
             'localization',
             'update.locale',
             'contentaccessible',
         ]