diff --git a/src/main/Main.coffee b/src/main/Main.coffee
index 5df1d4811..b987ac506 100644
--- a/src/main/Main.coffee
+++ b/src/main/Main.coffee
@@ -17,6 +17,9 @@ Main =
     try
       return if window.frameElement and window.frameElement.src is ''
 
+    # Don't run inside MathJax popups.
+    return if d.documentElement and not d.doctype
+
     # Detect multiple copies of 4chan X
     $.on d, '4chanXInitFinished', ->
       if Main.expectInitFinished