--- a/netwerk/base/nsStandardURL.cpp
+++ b/netwerk/base/nsStandardURL.cpp
@@ -22,16 +22,47 @@
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/ipc/URIUtils.h"
 #include <algorithm>
 #include "mozilla/dom/EncodingUtils.h"
 #include "nsContentUtils.h"
 #include "prprf.h"
 #include "nsReadableUtils.h"
 
+#ifdef MOZ_RUST_URLPARSE
+
+#include "RustURL.h"
+
+#define CALL_RUST_SETTER(func, ...)  \
+do {                                 \
+    mRustURL->func(__VA_ARGS__);     \
+    nsAutoCString rustSpec;          \
+    mRustURL->GetSpec(rustSpec);     \
+    if (mSpec != rustSpec) {         \
+        printf("Spec diff detected after setter (%s): rust: %s standard-url: %s\n", #func, rustSpec.get(), mSpec.get()); \
+    }                                \
+} while (0)
+
+#define CALL_RUST_GETTER_STR(result, func, ...)  \
+do {                                             \
+    nsAutoCString backup(result);                \
+    mRustURL->func(__VA_ARGS__);                 \
+    if (backup != result) {                      \
+        printf("Diff detected calling getter (%s): rust: %s standard-url: %s\n", #func, result.BeginReading() , backup.BeginReading()); \
+        result = backup;                  \
+    }                                            \
+} while (0)
+
+#else
+
+#define CALL_RUST_SETTER(func, ...)
+#define CALL_RUST_GETTER_STR(expected, func, ...)
+
+#endif // MOZ_RUST_URLPARSE
+
 using mozilla::dom::EncodingUtils;
 using namespace mozilla::ipc;
 
 namespace mozilla {
 namespace net {
 
 static NS_DEFINE_CID(kThisImplCID, NS_THIS_STANDARDURL_IMPL_CID);
 static NS_DEFINE_CID(kStandardURLCID, NS_STANDARDURL_CID);
@@ -272,16 +303,20 @@ nsStandardURL::nsStandardURL(bool aSuppo
     if (NS_IsMainThread()) {
         if (aTrackURL) {
             PR_APPEND_LINK(&mDebugCList, &gAllURLs);
         } else {
             PR_INIT_CLIST(&mDebugCList);
         }
     }
 #endif
+
+#ifdef MOZ_RUST_URLPARSE
+    mRustURL = new RustURL();
+#endif
 }
 
 nsStandardURL::~nsStandardURL()
 {
     LOG(("Destroying nsStandardURL @%p\n", this));
 
     if (mHostA) {
         free(mHostA);
@@ -1199,16 +1234,17 @@ NS_INTERFACE_MAP_END
 
 // result may contain unescaped UTF-8 characters
 NS_IMETHODIMP
 nsStandardURL::GetSpec(nsACString &result)
 {
     MOZ_ASSERT(mSpec.Length() <= (uint32_t) net_GetURLMaxLength(),
                "The spec should never be this long, we missed a check.");
     result = mSpec;
+    CALL_RUST_GETTER_STR(result, GetSpec, result);
     return NS_OK;
 }
 
 // result may contain unescaped UTF-8 characters
 NS_IMETHODIMP
 nsStandardURL::GetSensitiveInfoHiddenSpec(nsACString &result)
 {
     result = mSpec;
@@ -1495,16 +1531,18 @@ nsStandardURL::SetSpec(const nsACString 
         LOG((" path      = (%u,%d)\n", mPath.mPos,      mPath.mLen));
         LOG((" filepath  = (%u,%d)\n", mFilepath.mPos,  mFilepath.mLen));
         LOG((" directory = (%u,%d)\n", mDirectory.mPos, mDirectory.mLen));
         LOG((" basename  = (%u,%d)\n", mBasename.mPos,  mBasename.mLen));
         LOG((" extension = (%u,%d)\n", mExtension.mPos, mExtension.mLen));
         LOG((" query     = (%u,%d)\n", mQuery.mPos,     mQuery.mLen));
         LOG((" ref       = (%u,%d)\n", mRef.mPos,       mRef.mLen));
     }
+
+    CALL_RUST_SETTER(SetSpec, input);
     return rv;
 }
 
 NS_IMETHODIMP
 nsStandardURL::SetScheme(const nsACString &input)
 {
     ENSURE_MUTABLE();
 

--- a/netwerk/base/nsStandardURL.h
+++ b/netwerk/base/nsStandardURL.h
@@ -16,16 +16,17 @@
 #include "nsURLHelper.h"
 #include "nsIClassInfo.h"
 #include "nsISizeOf.h"
 #include "prclist.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/MemoryReporting.h"
 #include "nsIIPCSerializableURI.h"
 #include "nsISensitiveInfoHiddenURI.h"
+#include "RustURL.h"
 
 #ifdef NS_BUILD_REFCNT_LOGGING
 #define DEBUG_DUMP_URLS_AT_SHUTDOWN
 #endif
 
 class nsIBinaryInputStream;
 class nsIBinaryOutputStream;
 class nsIIDNService;
@@ -304,16 +305,20 @@ private:
     static bool                         gAlwaysEncodeInUTF8;
     static bool                         gEncodeQueryInUTF8;
 
 public:
 #ifdef DEBUG_DUMP_URLS_AT_SHUTDOWN
     PRCList mDebugCList;
     void PrintSpec() const { printf("  %s\n", mSpec.get()); }
 #endif
+
+#ifdef MOZ_RUST_URLPARSE
+    RefPtr<RustURL>                    mRustURL;
+#endif
 };
 
 #define NS_THIS_STANDARDURL_IMPL_CID                 \
 { /* b8e3e97b-1ccd-4b45-af5a-79596770f5d7 */         \
     0xb8e3e97b,                                      \
     0x1ccd,                                          \
     0x4b45,                                          \
     {0xaf, 0x5a, 0x79, 0x59, 0x67, 0x70, 0xf5, 0xd7} \