This code may help you:
Intent browserIntent = new Intent("android.intent.action.VIEW", Uri.parse("http://"));
ResolveInfo resolveInfo = getPackageManager().resolveActivity(browserIntent,PackageManager.MATCH_DEFAULT_ONLY);
// This is the default browser's packageName
String packageName = resolveInfo.activityInfo.packageName;
and if wanna start it, do as follows:
startActivity(getPackageManager().getLaunchIntentForPackage(packageName));