diff --git a/tools/build/build.py b/tools/build/build.py
index 913f23c8..b9df07d9 100755
--- a/tools/build/build.py
+++ b/tools/build/build.py
@@ -144,7 +144,8 @@ def build_oxjs(downloads=False, geo=False):
         ],
         [
             'Array.js', # Ox.slice (Collection.js) depends on Ox.toArray, salt (HTML.js) depends on Ox.range
-            'String.js' # salt (HTML.js) depends on Ox.char
+            'String.js', # salt (HTML.js) depends on Ox.char
+            'Type.js' # Ox.typeOf needed in Collection.js FF3.6 for Ox.slice fallback
         ],
         [
             'Collection.js', # Ox.PATH (Constants.js) depends on Ox.slice