Don't actually use Blob URL'd stylesheets, they don't get cleared automatically when navigating.

4chan_x.user.js

@@ -742,15 +742,10 @@
         return setTimeout($.asap, 25, test, cb);
       }
     },
-    addStyle: function(css, type) {
+    addStyle: function(css) {
       var style;
-      style = type === 'style' || !window.URL ? $.el('style', {
+      style = $.el('style', {
         textContent: css
-      }) : $.el('link', {
-        rel: 'stylesheet',
-        href: URL.createObjectURL(new Blob([css], {
-          type: 'text/css'
-        }))
       });
       $.asap((function() {
         return d.head;
@@ -4453,7 +4448,7 @@
         if (checked) {
           $.on(window, 'resize', ImageExpand.resize);
           if (!ImageExpand.style) {
-            ImageExpand.style = $.addStyle(null, 'style');
+            ImageExpand.style = $.addStyle(null);
           }
           return ImageExpand.resize();
         } else {

lib/$.coffee

@@ -88,14 +88,9 @@ $.extend $,
       cb()
     else
       setTimeout $.asap, 25, test, cb
-  addStyle: (css, type) ->
-    style = if type is 'style' or !window.URL
-      $.el 'style',
-        textContent: css
-    else
-      $.el 'link',
-        rel: 'stylesheet'
-        href: URL.createObjectURL new Blob([css], type: 'text/css')
+  addStyle: (css) ->
+    style = $.el 'style',
+      textContent: css
     $.asap (-> d.head), ->
       $.add d.head, style
     style

src/features.coffee

@@ -2948,7 +2948,7 @@ ImageExpand =
       if checked
         $.on window, 'resize', ImageExpand.resize
         unless ImageExpand.style
-          ImageExpand.style = $.addStyle null, 'style'
+          ImageExpand.style = $.addStyle null
         ImageExpand.resize()
       else
         $.off window, 'resize', ImageExpand.resize