diff --git a/brozzler/browser.py b/brozzler/browser.py
index 9c72589..4b602f1 100644
--- a/brozzler/browser.py
+++ b/brozzler/browser.py
@@ -658,11 +658,9 @@ class Browser:
     ):
         headers = extra_headers or {}
         headers["Accept-Encoding"] = "gzip"  # avoid encodings br, sdch
-        self.websock_thread.expect_result(self._command_id.peek())
         msg_id = self.send_to_chrome(
             method="Network.setExtraHTTPHeaders", params={"headers": headers}
         )
-        self._wait_for(lambda: self.websock_thread.received_result(msg_id), timeout=10)
         if user_agent:
             msg_id = self.send_to_chrome(
                 method="Network.setUserAgentOverride", params={"userAgent": user_agent}
diff --git a/brozzler/worker.py b/brozzler/worker.py
index 116bb75..1d238a1 100644
--- a/brozzler/worker.py
+++ b/brozzler/worker.py
@@ -414,7 +414,7 @@ class BrozzlerWorker:
             self.logger.trace("%r", chrome_msg)
             if chrome_msg.get("params", {}).get("versions"):
                 url = chrome_msg.get("params", {}).get("versions")[0].get("scriptURL")
-                if url and url not in sw_fetched:
+                if url and url.startswith('http') and url not in sw_fetched:
                     self.logger.info("fetching service worker script %s", url)
                     self._fetch_url(site, url=url)
                     sw_fetched.add(url)