diff --git a/tools/bundler.js b/tools/bundler.js
index 4f18f57fa7..00de0b103b 100644
--- a/tools/bundler.js
+++ b/tools/bundler.js
@@ -940,17 +940,6 @@ _.extend(ClientTarget.prototype, {
 
         // Use a SHA to make this cacheable.
         var sourceMapBaseName = file.hash() + ".map";
-        // XXX When we can, drop all of this and just use the SourceMap
-        //     header. FF doesn't support that yet, though:
-        //         https://bugzilla.mozilla.org/show_bug.cgi?id=765993
-        // Note: if we use the older '//@' comment, FF 24 will print a lot
-        // of warnings to the console. So we use the newer '//#' comment...
-        // which Chrome (28) doesn't support. So we also set X-SourceMap
-        // in webapp_server.
-        file.setContents(Buffer.concat([
-          file.contents(),
-          new Buffer("\n//# sourceMappingURL=" + sourceMapBaseName + "\n")
-        ]));
         manifestItem.sourceMapUrl = require('url').resolve(
           file.url, sourceMapBaseName);
       }
@@ -1200,12 +1189,6 @@ _.extend(JsImage.prototype, {
           { data: new Buffer(item.sourceMap, 'utf8') }
         );
 
-        var sourceMapFileName = path.basename(loadItem.sourceMap);
-        // Remove any existing sourceMappingURL line. (eg, if roundtripping
-        // through JsImage.readFromDisk, don't end up with two!)
-        item.source = item.source.replace(
-            /\n\/\/# sourceMappingURL=.+\n?$/, '');
-        item.source += "\n//# sourceMappingURL=" + sourceMapFileName + "\n";
         loadItem.sourceMapRoot = item.sourceMapRoot;
       }