diff --git a/src/main/Main.coffee b/src/main/Main.coffee
index 93ded5a02..9b600b920 100644
--- a/src/main/Main.coffee
+++ b/src/main/Main.coffee
@@ -99,6 +99,7 @@ Main =
 
         # Fresh install
         else if !items.previousversion?
+          Main.isFirstRun = true
           Main.ready ->
             $.set 'previousversion', g.VERSION
             Settings.open()
@@ -502,6 +503,16 @@ Main =
       new Notice 'error', 'Error: Multiple copies of 4chan X are enabled.'
       $.addClass doc, 'tainted'
 
+    # Detect conflicts with native extension
+    if g.SITE.testNativeExtension and not $.hasClass(doc, 'tainted')
+      {enabled} = g.SITE.testNativeExtension()
+      if enabled
+        $.addClass doc, 'tainted'
+        if Conf['Disable Native Extension'] and !Main.isFirstRun
+          msg = $.el 'div',
+            <%= html('Failed to disable the native extension. You may need to <a href="' + meta.faq + '#blocking-native-extension" target="_blank">block it</a>.') %>
+          new Notice 'error', msg
+
     unless errors instanceof Array
       error = errors
     else if errors.length is 1
diff --git a/src/site/SW.yotsuba.coffee b/src/site/SW.yotsuba.coffee
index 44521b85a..c29f51cfe 100644
--- a/src/site/SW.yotsuba.coffee
+++ b/src/site/SW.yotsuba.coffee
@@ -225,3 +225,7 @@ SW.yotsuba =
 
   isLinkified: (link) ->
     ImageHost.test(link.hostname)
+
+  testNativeExtension: ->
+    $.global ->
+      @enabled = 'true' if window.Parser.postMenuIcon