diff --git a/IPython/html/static/notebook/less/codemirror.less b/IPython/html/static/notebook/less/codemirror.less
index aa440e2..fa9759c 100644
--- a/IPython/html/static/notebook/less/codemirror.less
+++ b/IPython/html/static/notebook/less/codemirror.less
@@ -22,14 +22,6 @@
     overflow-x: auto;
 }
 
-@-moz-document url-prefix() {
-    /* Firefox does weird and terrible things (#3549) when overflow-x is auto */
-    /* It doesn't respect the overflow setting anyway, so we can workaround it with this */
-    .CodeMirror-scroll {
-        overflow-x: hidden;
-    }
-}
-
 .CodeMirror-lines {
     /* In CM2, this used to be 0.4em, but in CM3 it went to 4px. We need the em value because */
     /* we have set a different line-height and want this to scale with that. */