--- a/docshell/test/browser/browser.ini
+++ b/docshell/test/browser/browser.ini
@@ -25,16 +25,18 @@ support-files =
   file_bug234628-8-child.html
   file_bug234628-8.html
   file_bug234628-9-child.html
   file_bug234628-9.html
   file_bug420605.html
   file_bug503832.html
   file_bug655270.html
   file_bug670318.html
+  file_bug852909.pdf
+  file_bug852909.png
   file_bug941562-child.html
   file_bug941562.html
   print_postdata.sjs
   test-form_sjis.html
 
 [browser_bug134911.js]
 [browser_bug234628-1.js]
 [browser_bug234628-10.js]
@@ -54,13 +56,14 @@ support-files =
 [browser_bug422543.js]
 [browser_bug441169.js]
 [browser_bug503832.js]
 [browser_bug554155.js]
 [browser_bug655270.js]
 [browser_bug655273.js]
 [browser_bug670318.js]
 [browser_bug673467.js]
+[browser_bug852909.js]
 [browser_bug92473.js]
 [browser_bug941562.js]
 [browser_loadDisallowInherit.js]
 [browser_loadURI.js]
 [browser_search_notification.js]

new file mode 100644
--- /dev/null
+++ b/docshell/test/browser/browser_bug852909.js
@@ -0,0 +1,33 @@
+var rootDir = "http://mochi.test:8888/browser/docshell/test/browser/";
+
+function test() {
+  waitForExplicitFinish();
+
+  gBrowser.selectedTab = gBrowser.addTab(rootDir + "file_bug852909.png");
+  gBrowser.selectedBrowser.addEventListener("load", image, true);
+}
+
+function image(event) {
+  if (event.target != gBrowser.contentDocument) {
+    return;
+  }
+  gBrowser.selectedBrowser.removeEventListener("load", image, true);
+
+  ok(!gBrowser.docShell.mayEnableCharacterEncodingMenu, "Docshell should say the menu should be disabled for images.");
+
+  gBrowser.removeCurrentTab();
+  gBrowser.selectedTab = gBrowser.addTab(rootDir + "file_bug852909.pdf");
+  gBrowser.selectedBrowser.addEventListener("load", pdf, true);
+}
+
+function pdf(event) {
+  if (event.target != gBrowser.contentDocument) {
+    return;
+  }
+  gBrowser.selectedBrowser.removeEventListener("load", pdf, true);
+
+  ok(!gBrowser.docShell.mayEnableCharacterEncodingMenu, "Docshell should say the menu should be disabled for PDF.js.");
+
+  gBrowser.removeCurrentTab();
+  finish();
+}

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