Don't report firefox crash reports

tools/testing/dart/browser_controller.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 library browser;
 
 import "dart:async";
 import "dart:convert" show LineSplitter, UTF8, JSON;
 import "dart:core";
 import "dart:io";
 
@@ skipping 726 matching lines @@
         return new Future.value(false);
       }
       version = versionResult.stdout;
       _logEvent("Got version: $version");
 
       return Directory.systemTemp.createTemp().then((userDir) {
         _createPreferenceFile(userDir.path);
         _cleanup = () { userDir.deleteSync(recursive: true); };
         var args = ["-profile", "${userDir.path}",
                     "-no-remote", "-new-instance", url];
-        return startBrowser(_binary, args);
+        var environment = new Map<String,String>.from(Platform.environment);
+        environment["MOZ_CRASHREPORTER_DISABLE"] = "1";
+        return startBrowser(_binary, args, environment: environment);
 
       });
     }).catchError((e) {
       _logEvent("Running $_binary --version failed with $e");
       return false;
     });
   }
 
   String toString() => "Firefox";
 }
@@ skipping 1036 matching lines @@
     </div>
     <div id="embedded_iframe_div" class="test box">
       <iframe style="width:100%;height:100%;" id="embedded_iframe"></iframe>
     </div>
   </body>
 </html>
 """;
     return driverContent;
   }
 }