diff --git a/modules/libpr0n/test/mochitest/Makefile.in b/modules/libpr0n/test/mochitest/Makefile.in
index fd4b258d5945..ac31cf1de694 100644
--- a/modules/libpr0n/test/mochitest/Makefile.in
+++ b/modules/libpr0n/test/mochitest/Makefile.in
@@ -62,6 +62,9 @@ _TEST_FILES =   imgutils.js \
                 bug496292-iframe-2.html \
                 bug496292-1.sjs \
                 bug496292-2.sjs \
+                test_bug512435.html \
+                damon.jpg \
+                shaver.png \
 		$(NULL)
 
 libs:: $(_TEST_FILES)
diff --git a/modules/libpr0n/test/mochitest/damon.jpg b/modules/libpr0n/test/mochitest/damon.jpg
new file mode 100644
index 000000000000..917b336607fb
Binary files /dev/null and b/modules/libpr0n/test/mochitest/damon.jpg differ
diff --git a/modules/libpr0n/test/mochitest/imgutils.js b/modules/libpr0n/test/mochitest/imgutils.js
index 55f9741fb90b..87681cba0aa1 100644
--- a/modules/libpr0n/test/mochitest/imgutils.js
+++ b/modules/libpr0n/test/mochitest/imgutils.js
@@ -3,6 +3,15 @@
 // Note that this is use by tests elsewhere in the source tree. When in doubt,
 // check mxr before removing or changing functionality.
 
+// Helper function to clear the image cache of content images
+function clearImageCache()
+{
+  netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
+  var imageCache = Components.classes["@mozilla.org/image/cache;1"]
+                             .getService(Components.interfaces.imgICache);
+  imageCache.clearCache(false); // true=chrome, false=content
+}
+
 // Helper function to determine if the frame is decoded for a given image id
 function isFrameDecoded(id)
 {
diff --git a/modules/libpr0n/test/mochitest/shaver.png b/modules/libpr0n/test/mochitest/shaver.png
new file mode 100644
index 000000000000..ab0b6c7b4017
Binary files /dev/null and b/modules/libpr0n/test/mochitest/shaver.png differ
diff --git a/modules/libpr0n/test/mochitest/test_bug512435.html b/modules/libpr0n/test/mochitest/test_bug512435.html
new file mode 100644
index 000000000000..3e698de10606
--- /dev/null
+++ b/modules/libpr0n/test/mochitest/test_bug512435.html
@@ -0,0 +1,50 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=512435
+-->
+<head>
+  <title>Test for Bug 512435</title>
+  <script type="application/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="/tests/modules/libpr0n/test/mochitest/imgutils.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=512435">Mozilla Bug 512435</a>
+<img id="img_a">
+<img id="img_b">
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+// Boilerplate
+netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
+const Ci = Components.interfaces;
+const Cc = Components.classes;
+SimpleTest.waitForExplicitFinish();
+
+// We're relying on very particular behavior for certain images - clear the
+// image cache, _then_ set src
+clearImageCache();
+document.getElementById("img_a").src = "damon.jpg";
+document.getElementById("img_b").src = "shaver.png";
+
+// Our handler
+function loadHandler() {
+
+  // The two images should be decoded
+  ok(isFrameDecoded("img_a"), "img_a should be decoded before onload fires");
+  ok(isFrameDecoded("img_b"), "img_b should be decoded before onload fires");
+
+  // All done
+  SimpleTest.finish();
+}
+
+// Set our onload handler
+window.onload = loadHandler;
+
+</script>
+</pre>
+</body>
+</html>
