--- a/caps/OriginAttributes.cpp
+++ b/caps/OriginAttributes.cpp
@@ -8,19 +8,16 @@
 #include "mozilla/Preferences.h"
 #include "mozilla/dom/BlobURLProtocolHandler.h"
 #include "mozilla/dom/URLSearchParams.h"
 #include "mozilla/dom/quota/QuotaManager.h"
 #include "nsIEffectiveTLDService.h"
 #include "nsIURI.h"
 #include "nsURLHelper.h"
 
-static const char kSourceChar = ':';
-static const char kSanitizedChar = '+';
-
 namespace mozilla {
 
 using dom::URLParams;
 
 void OriginAttributes::SetFirstPartyDomain(const bool aIsTopLevelDocument,
                                            nsIURI* aURI, bool aForced) {
   bool isFirstPartyEnabled = IsFirstPartyEnabled();
 
@@ -143,26 +140,27 @@ void OriginAttributes::CreateSuffix(nsAC
   if (mPrivateBrowsingId) {
     value.Truncate();
     value.AppendInt(mPrivateBrowsingId);
     params.Set(NS_LITERAL_STRING("privateBrowsingId"), value);
   }
 
   if (!mFirstPartyDomain.IsEmpty()) {
     nsAutoString sanitizedFirstPartyDomain(mFirstPartyDomain);
-    sanitizedFirstPartyDomain.ReplaceChar(kSourceChar, kSanitizedChar);
+    sanitizedFirstPartyDomain.ReplaceChar(
+        dom::quota::QuotaManager::kReplaceChars, '+');
 
     params.Set(NS_LITERAL_STRING("firstPartyDomain"),
                sanitizedFirstPartyDomain);
   }
 
   if (!mGeckoViewSessionContextId.IsEmpty()) {
     nsAutoString sanitizedGeckoViewUserContextId(mGeckoViewSessionContextId);
     sanitizedGeckoViewUserContextId.ReplaceChar(
-        dom::quota::QuotaManager::kReplaceChars, kSanitizedChar);
+        dom::quota::QuotaManager::kReplaceChars, '+');
 
     params.Set(NS_LITERAL_STRING("geckoViewUserContextId"),
                sanitizedGeckoViewUserContextId);
   }
 
   aStr.Truncate();
 
   params.Serialize(value);
@@ -240,19 +238,17 @@ class MOZ_STACK_CLASS PopulateFromSuffix
       NS_ENSURE_TRUE(val >= 0 && val <= UINT32_MAX, false);
       mOriginAttributes->mPrivateBrowsingId = static_cast<uint32_t>(val);
 
       return true;
     }
 
     if (aName.EqualsLiteral("firstPartyDomain")) {
       MOZ_RELEASE_ASSERT(mOriginAttributes->mFirstPartyDomain.IsEmpty());
-      nsAutoString firstPartyDomain(aValue);
-      firstPartyDomain.ReplaceChar(kSanitizedChar, kSourceChar);
-      mOriginAttributes->mFirstPartyDomain.Assign(firstPartyDomain);
+      mOriginAttributes->mFirstPartyDomain.Assign(aValue);
       return true;
     }
 
     if (aName.EqualsLiteral("geckoViewUserContextId")) {
       MOZ_RELEASE_ASSERT(
           mOriginAttributes->mGeckoViewSessionContextId.IsEmpty());
       mOriginAttributes->mGeckoViewSessionContextId.Assign(aValue);
       return true;

--- a/caps/tests/gtest/TestOriginAttributes.cpp
+++ b/caps/tests/gtest/TestOriginAttributes.cpp
@@ -21,18 +21,16 @@ static void TestSuffix(const OriginAttri
 }
 
 static void TestFPD(const nsAString& spec, const nsAString& fpd) {
   OriginAttributes attrs;
   nsCOMPtr<nsIURI> url;
   ASSERT_EQ(NS_NewURI(getter_AddRefs(url), spec), NS_OK);
   attrs.SetFirstPartyDomain(true, url);
   EXPECT_TRUE(attrs.mFirstPartyDomain.Equals(fpd));
-
-  TestSuffix(attrs);
 }
 
 TEST(OriginAttributes, Suffix_default)
 {
   OriginAttributes attrs;
   TestSuffix(attrs);
 }