Disable crash reporting on Firefox.

lib/src/runner/browser/firefox.dart

 // Copyright (c) 2015, 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 test.runner.browser.firefox;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
@@ skipping 47 matching lines @@
     withTempDir((dir) {
       _dir = dir;
 
       new File(p.join(dir, 'prefs.js')).writeAsStringSync(_preferences);
 
       return Process.start(executable, [
         "--profile",
         "$_dir",
         url.toString(),
         "--no-remote"
-      ]).then((process) {
+      ], environment: {
+        "MOZ_CRASHREPORTER_DISABLE": "1"
+      }).then((process) {
         _process = process;
         _onProcessStartedCompleter.complete();
 
         // TODO(nweiz): the browser's standard output is almost always useless
         // noise, but we should allow the user to opt in to seeing it.
         return _process.exitCode;
       });
     }).then((exitCode) {
       if (exitCode != 0) throw "Firefox failed with exit code $exitCode.";
     }).then(_onExitCompleter.complete)
@@ skipping 27 matching lines @@
 
       var path = p.join(prefix, suffix);
       if (new File(p.join(prefix, suffix)).existsSync()) return path;
     }
 
     // Fall back on looking it up on the path. This probably won't work, but at
     // least it will fail with a useful error message.
     return "firefox.exe";
   }
 }