diff --git a/ox/cache.py b/ox/cache.py
index b5f9a9e..c359cbd 100644
--- a/ox/cache.py
+++ b/ox/cache.py
@@ -102,6 +102,8 @@ def read_url(url, data=None, headers=None, timeout=cache_timeout, valid=None, un
     url_headers = {}
     if not result:
         if USE_REQUESTS:
+            if headers is None:
+                headers = DEFAULT_HEADERS.copy()
             r = requests_session.get(url, headers=headers)
             for key in r.headers:
                 url_headers[key.lower()] = r.headers[key]
diff --git a/ox/net.py b/ox/net.py
index 59e6abe..3a07d91 100644
--- a/ox/net.py
+++ b/ox/net.py
@@ -21,7 +21,7 @@ from chardet.universaldetector import UniversalDetector
 DEBUG = False
 # Default headers for HTTP requests.
 DEFAULT_HEADERS = {
-    'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64; rv:69.0) Gecko/20100101 Firefox/69.0',
+    'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0',
     'Accept-Charset': 'ISO-8859-1,utf-8;q=0.7,*;q=0.7',
     'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
     'Accept-Language': 'en-US,en;q=0.8,fr;q=0.6,de;q=0.4',