diff --git a/netwerk/base/nsNetUtil.cpp b/netwerk/base/nsNetUtil.cpp
index 769afb2f68a92..4c03cf63c3122 100644
--- a/netwerk/base/nsNetUtil.cpp
+++ b/netwerk/base/nsNetUtil.cpp
@@ -1862,18 +1862,10 @@ nsresult NS_NewURI(nsIURI** aURI, const nsACString& aSpec,
   }
 
   if (scheme.EqualsLiteral("file")) {
-    nsAutoCString buf(aSpec);
-#if defined(XP_WIN)
-    buf.Truncate();
-    if (!net_NormalizeFileURL(aSpec, buf)) {
-      buf = aSpec;
-    }
-#endif
-
     return NS_MutateURI(new nsStandardURL::Mutator())
         .Apply(&nsIFileURLMutator::MarkFileURL)
         .Apply(&nsIStandardURLMutator::Init,
-               nsIStandardURL::URLTYPE_NO_AUTHORITY, -1, buf, aCharset,
+               nsIStandardURL::URLTYPE_NO_AUTHORITY, -1, aSpec, aCharset,
                aBaseURI, nullptr)
         .Finalize(aURI);
   }
diff --git a/netwerk/base/nsURLHelper.cpp b/netwerk/base/nsURLHelper.cpp
index 41bf0aa97762e..3850c6865a742 100644
--- a/netwerk/base/nsURLHelper.cpp
+++ b/netwerk/base/nsURLHelper.cpp
@@ -516,6 +516,11 @@ bool net_NormalizeFileURL(const nsACString& aURL, nsCString& aResultBuf) {
       aResultBuf += '/';
       begin = s + 1;
     }
+    if (*s == '#') {
+      // Don't normalize any backslashes following the hash.
+      s = endIter.get();
+      break;
+    }
   }
   if (writing && s > begin) aResultBuf.Append(begin, s - begin);
 
diff --git a/netwerk/test/unit/test_URIs.js b/netwerk/test/unit/test_URIs.js
index 0f53b1fc4a1b8..b9ec2b3f2d486 100644
--- a/netwerk/test/unit/test_URIs.js
+++ b/netwerk/test/unit/test_URIs.js
@@ -966,3 +966,15 @@ add_task(async function round_trip_invalid_ace_label() {
     uri = Services.io.newURI("http://a.b.c.XN--pokxncvks");
   }, /NS_ERROR_MALFORMED_URI/);
 });
+
+add_task(async function test_bug1843717() {
+  // Make sure file path normalization on windows
+  // doesn't affect the hash of the URL.
+  let base = Services.io.newURI("file:///abc\\def/");
+  let uri = Services.io.newURI("foo\\bar#x\\y", null, base);
+  Assert.equal(uri.spec, "file:///abc/def/foo/bar#x\\y");
+  uri = Services.io.newURI("foo\\bar#xy", null, base);
+  Assert.equal(uri.spec, "file:///abc/def/foo/bar#xy");
+  uri = Services.io.newURI("foo\\bar#", null, base);
+  Assert.equal(uri.spec, "file:///abc/def/foo/bar#");
+});