Use a closure with a private variable for $.cache's requests.

4chan_x.user.js

@@ -369,9 +369,11 @@
       r.send(form);
       return r;
     },
-    cache: function(url, cb) {
-      var req, reqs, _base;
-      reqs = (_base = $.cache).requests || (_base.requests = {});
+    cache: (function() {
+      var reqs;
+      reqs = {};
+      return function(url, cb) {
+        var req;
         if (req = reqs[url]) {
           if (req.readyState === 4) {
             cb.call(req);
@@ -399,7 +401,8 @@
         });
         req.callbacks = [cb];
         return reqs[url] = req;
-    },
+      };
+    })(),
     cb: {
       checked: function() {
         $.set(this.name, this.checked);

script.coffee

@@ -295,8 +295,9 @@ $.extend $,
     $.extend r.upload, upCallbacks
     r.send form
     r
-  cache: (url, cb) ->
-    reqs = $.cache.requests or= {}
+  cache: (->
+    reqs = {}
+    (url, cb) ->
       if req = reqs[url]
         if req.readyState is 4
           cb.call req
@@ -311,6 +312,7 @@ $.extend $,
         onerror: -> delete reqs[url]
       req.callbacks = [cb]
       reqs[url] = req
+  )()
   cb:
     checked: ->
       $.set @name, @checked