Added xnxx.com's alternative domain support.
diff --git a/yt_dlp/extractor/xnxx.py b/yt_dlp/extractor/xnxx.py
index dd4fb54d463..27f99162778 100644
--- a/yt_dlp/extractor/xnxx.py
+++ b/yt_dlp/extractor/xnxx.py
@@ -13,7 +13,7 @@
 
 
 class XNXXIE(InfoExtractor):
-    _VALID_URL = r'https?://(?:video|www)\.xnxx\.com/video-?(?P<id>[0-9a-z]+)/'
+    _VALID_URL = r'https?://(?:video|www)\.xnxx3?\.com/video-?(?P<id>[0-9a-z]+)/'
     _TESTS = [{
         'url': 'http://www.xnxx.com/video-55awb78/skyrim_test_video',
         'md5': '7583e96c15c0f21e9da3453d9920fbba',
@@ -32,6 +32,9 @@ class XNXXIE(InfoExtractor):
     }, {
         'url': 'http://www.xnxx.com/video-55awb78/',
         'only_matching': True,
+    }, {
+        'url': 'http://www.xnxx3.com/video-55awb78/',
+        'only_matching': True,
     }]
 
     def _real_extract(self, url):

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