diff --git a/src/General/Index.coffee b/src/General/Index.coffee
index 8b614384e..90ade98ae 100644
--- a/src/General/Index.coffee
+++ b/src/General/Index.coffee
@@ -594,11 +594,11 @@ Index =
       location.reload()
       return
 
-    Index.req = $.ajax "#{location.protocol}//a.4cdn.org/#{g.BOARD}/catalog.json",
-      onloadend: Index.load
-    ,
-      whenModified: 'Index'
-      bypassCache: true
+    Index.req = $.whenModified(
+      Site.urls.catalogJSON({boardID: g.BOARD.ID}),
+      'Index',
+      Index.load
+    )
     $.addClass Index.button, 'fa-spin'
 
   load: ->
diff --git a/src/Monitoring/ThreadStats.coffee b/src/Monitoring/ThreadStats.coffee
index ca210334d..014cd8a67 100644
--- a/src/Monitoring/ThreadStats.coffee
+++ b/src/Monitoring/ThreadStats.coffee
@@ -75,9 +75,11 @@ ThreadStats =
       $.addClass ThreadStats.pageCountEl, 'warning'
       return
     ThreadStats.timeout = setTimeout ThreadStats.fetchPage, 2 * $.MINUTE
-    $.ajax "#{location.protocol}//a.4cdn.org/#{ThreadStats.thread.board}/threads.json", onload: ThreadStats.onThreadsLoad,
-      whenModified: 'ThreadStats'
-      bypassCache:  true
+    $.whenModified(
+      Site.urls.threadsListJSON({boardID: ThreadStats.thread.board}),
+      'ThreadStats',
+      ThreadStats.onThreadsLoad
+    )
 
   onThreadsLoad: ->
     if @status is 200
diff --git a/src/Monitoring/ThreadUpdater.coffee b/src/Monitoring/ThreadUpdater.coffee
index c44851170..c3151569c 100644
--- a/src/Monitoring/ThreadUpdater.coffee
+++ b/src/Monitoring/ThreadUpdater.coffee
@@ -231,12 +231,12 @@ ThreadUpdater =
     clearTimeout ThreadUpdater.timeoutID
     ThreadUpdater.set 'timer', '...', 'loading'
     ThreadUpdater.req?.abort()
-    ThreadUpdater.req = $.ajax "#{location.protocol}//a.4cdn.org/#{ThreadUpdater.thread.board}/thread/#{ThreadUpdater.thread}.json",
-      onloadend: ThreadUpdater.cb.load
-      timeout:   $.MINUTE
-    ,
-      whenModified: 'ThreadUpdater'
-      bypassCache:  true
+    ThreadUpdater.req = $.whenModified(
+      Site.urls.threadJSON({boardID: ThreadUpdater.thread.board.ID, threadID: ThreadUpdater.thread.ID}),
+      'ThreadUpdater',
+      ThreadUpdater.cb.load,
+      {timeout: $.MINUTE}
+    )
 
   updateThreadStatus: (type, status) ->
     return if not (hasChanged = ThreadUpdater.thread["is#{type}"] isnt status)
diff --git a/src/Monitoring/ThreadWatcher.coffee b/src/Monitoring/ThreadWatcher.coffee
index 0f72de536..da6d04a4a 100644
--- a/src/Monitoring/ThreadWatcher.coffee
+++ b/src/Monitoring/ThreadWatcher.coffee
@@ -174,7 +174,6 @@ ThreadWatcher =
     if ThreadWatcher.requests.length is 0
       ThreadWatcher.status.textContent = '...'
       $.addClass ThreadWatcher.refreshButton, 'fa-spin'
-    ajax = if (siteID is Site.hostname) then $.ajax else CrossOrigin.ajax
     onloadend = ->
       return if @finished
       @finished = true
@@ -184,11 +183,19 @@ ThreadWatcher =
       else
         ThreadWatcher.status.textContent = "#{Math.round(ThreadWatcher.fetched / ThreadWatcher.requests.length * 100)}%"
       cb.apply @, args
-    req = ajax url,
-      onloadend: onloadend
-      timeout: $.MINUTE
-    ,
-      whenModified: if force then false else 'ThreadWatcher'
+    if siteID is Site.hostname
+      if force
+        delete $.lastModified.ThreadWatcher?[url]
+      req = $.whenModified(
+        url,
+        'ThreadWatcher',
+        onloadend,
+        {timeout: $.MINUTE}
+      )
+    else
+      req = CrossOrigin.ajax url,
+        onloadend: onloadend
+        timeout: $.MINUTE
     ThreadWatcher.requests.push req
 
   clearRequests: ->
diff --git a/src/platform/$.coffee b/src/platform/$.coffee
index 24ddde8c6..8e7772478 100644
--- a/src/platform/$.coffee
+++ b/src/platform/$.coffee
@@ -41,34 +41,22 @@ $.extend = (object, properties) ->
   return
 
 $.ajax = do ->
-  # Status Code 304: Not modified
-  # With the `If-Modified-Since` header we only receive the HTTP headers and no body for 304 responses.
-  # This saves a lot of bandwidth and CPU time for both the users and the servers.
-  lastModified = {}
   if window.wrappedJSObject and not XMLHttpRequest.wrappedJSObject
     pageXHR = XPCNativeWrapper window.wrappedJSObject.XMLHttpRequest
   else
     pageXHR = XMLHttpRequest
 
   (url, options={}, extra={}) ->
-    {type, whenModified, bypassCache, upCallbacks, form} = extra
+    {type, upCallbacks, form, headers} = extra
     options.responseType ?= 'json'
     # XXX https://forums.lanik.us/viewtopic.php?f=64&t=24173&p=78310
     url = url.replace /^((?:https?:)?\/\/(?:\w+\.)?4c(?:ha|d)n\.org)\/adv\//, '$1//adv/'
-    if whenModified
-      params = []
-      # XXX https://bugs.chromium.org/p/chromium/issues/detail?id=643659
-      params.push "s=#{whenModified}" if $.engine is 'blink'
-      params.push "t=#{Date.now()}" if Site.software is 'yotsuba' and bypassCache
-      url0 = url
-      url += '?' + params.join('&') if params.length
     r = new pageXHR()
     type or= form and 'post' or 'get'
     try
       r.open type, url, true
-      if whenModified
-        r.setRequestHeader 'If-Modified-Since', lastModified[whenModified][url0] if lastModified[whenModified]?[url0]?
-        $.on r, 'load', -> (lastModified[whenModified] or= {})[url0] = r.getResponseHeader 'Last-Modified'
+      for key, value of (headers or {})
+        r.setRequestHeader key, value
       $.extend r, options
       $.extend r.upload, upCallbacks
       # connection error or content blocker
@@ -89,6 +77,29 @@ $.ajax = do ->
         $.queueTask $.event, event, null, r
     r
 
+# Status Code 304: Not modified
+# With the `If-Modified-Since` header we only receive the HTTP headers and no body for 304 responses.
+# This saves a lot of bandwidth and CPU time for both the users and the servers.
+$.lastModified = {}
+$.whenModified = (url, bucket, cb, options={}) ->
+  {timeout} = options
+  params = []
+  # XXX https://bugs.chromium.org/p/chromium/issues/detail?id=643659
+  params.push "s=#{bucket}" if $.engine is 'blink'
+  params.push "t=#{Date.now()}" if Site.software is 'yotsuba'
+  url0 = url
+  url += '?' + params.join('&') if params.length
+  headers = {}
+  if (t = $.lastModified[bucket]?[url0])?
+    headers['If-Modified-Since'] = t
+  r = $.ajax url, {
+    onloadend: ->
+      ($.lastModified[bucket] or= {})[url0] = @getResponseHeader('Last-Modified')
+      cb.call @
+    timeout
+  }, {headers}
+  r
+
 do ->
   reqs = {}
   $.cache = (url, cb, options={}) ->