diff --git a/url/setters_tests.json b/url/setters_tests.json
index 3d24725156b3da..fa40ddafe5abef 100644
--- a/url/setters_tests.json
+++ b/url/setters_tests.json
@@ -1613,6 +1613,33 @@
                 "href": "sc://example.net/%23",
                 "pathname": "/%23"
             }
+        },
+        {
+            "comment": "File URLs and (back)slashes",
+            "href": "file://monkey/",
+            "new_value": "\\\\",
+            "expected": {
+                "href": "file://monkey/",
+                "pathname": "/"
+            }
+        },
+        {
+            "comment": "File URLs and (back)slashes",
+            "href": "file:///unicorn",
+            "new_value": "//\\/",
+            "expected": {
+                "href": "file:///",
+                "pathname": "/"
+            }
+        },
+        {
+            "comment": "File URLs and (back)slashes",
+            "href": "file:///unicorn",
+            "new_value": "//monkey/..//",
+            "expected": {
+                "href": "file:///",
+                "pathname": "/"
+            }
         }
     ],
     "search": [
diff --git a/url/urltestdata.json b/url/urltestdata.json
index 6bc9c65e61b561..f695418964bb77 100644
--- a/url/urltestdata.json
+++ b/url/urltestdata.json
@@ -5137,6 +5137,175 @@
     "search": "?test",
     "hash": "#x"
   },
+  "# File URLs and many (back)slashes",
+  {
+    "input": "file:\\\\//",
+    "base": "about:blank",
+    "href": "file:///",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "",
+    "hostname": "",
+    "port": "",
+    "pathname": "/",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "file:\\\\\\\\",
+    "base": "about:blank",
+    "href": "file:///",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "",
+    "hostname": "",
+    "port": "",
+    "pathname": "/",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "file://spider///",
+    "base": "about:blank",
+    "href": "file://spider/",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "spider",
+    "hostname": "spider",
+    "port": "",
+    "pathname": "/",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "file:\\\\localhost//",
+    "base": "about:blank",
+    "href": "file:///",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "",
+    "hostname": "",
+    "port": "",
+    "pathname": "/",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "file:///localhost//cat",
+    "base": "about:blank",
+    "href": "file:///localhost//cat",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "",
+    "hostname": "",
+    "port": "",
+    "pathname": "/localhost//cat",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "file://\\/localhost//cat",
+    "base": "about:blank",
+    "href": "file:///localhost//cat",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "",
+    "hostname": "",
+    "port": "",
+    "pathname": "/localhost//cat",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "file://localhost//a//../..//",
+    "base": "about:blank",
+    "href": "file:///",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "",
+    "hostname": "",
+    "port": "",
+    "pathname": "/",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "/////mouse",
+    "base": "file:///elephant",
+    "href": "file:///mouse",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "",
+    "hostname": "",
+    "port": "",
+    "pathname": "/mouse",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "\\//pig",
+    "base": "file://lion/",
+    "href": "file:///pig",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "",
+    "hostname": "",
+    "port": "",
+    "pathname": "/pig",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "\\/localhost//pig",
+    "base": "file://lion/",
+    "href": "file:///pig",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "",
+    "hostname": "",
+    "port": "",
+    "pathname": "/pig",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "//localhost//pig",
+    "base": "file://lion/",
+    "href": "file:///pig",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "",
+    "hostname": "",
+    "port": "",
+    "pathname": "/pig",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "/..//localhost//pig",
+    "base": "file://lion/",
+    "href": "file://lion/localhost//pig",
+    "protocol": "file:",
+    "username": "",
+    "password": "",
+    "host": "lion",
+    "hostname": "lion",
+    "port": "",
+    "pathname": "/localhost//pig",
+    "search": "",
+    "hash": ""
+  },
   "# Windows drive letter quirk with not empty host",
   {
     "input": "file://example.net/C:/",