diff --git a/docshell/base/nsDefaultURIFixup.cpp b/docshell/base/nsDefaultURIFixup.cpp
index 77e008b15a17..a1a893b8efb2 100644
--- a/docshell/base/nsDefaultURIFixup.cpp
+++ b/docshell/base/nsDefaultURIFixup.cpp
@@ -687,7 +687,7 @@ nsDefaultURIFixup::FixupURIProtocol(const nsACString& aURIString,
   //   no-scheme.com/query?foo=http://www.foo.com
   //   user:pass@no-scheme.com
   //
-  int32_t schemeDelim = uriString.Find("://", 0);
+  int32_t schemeDelim = uriString.Find("://");
   int32_t firstDelim = uriString.FindCharInSet("/:");
   if (schemeDelim <= 0 ||
       (firstDelim != -1 && schemeDelim > firstDelim)) {
diff --git a/dom/media/gmp/ChromiumCDMChild.cpp b/dom/media/gmp/ChromiumCDMChild.cpp
index e99f913622ab..8dc288b4c57e 100644
--- a/dom/media/gmp/ChromiumCDMChild.cpp
+++ b/dom/media/gmp/ChromiumCDMChild.cpp
@@ -232,7 +232,7 @@ ChromiumCDMChild::OnResolveNewSessionPromiseInternal(uint32_t aPromiseId,
     // a session it calls OnResolveNewSessionPromise with nullptr as the sessionId.
     // We can safely assume this means that we have failed to load a session
     // as the other methods specify calling 'OnRejectPromise' when they fail.
-    bool loadSuccessful = aSessionId != nullptr;
+    bool loadSuccessful = !aSessionId.IsEmpty();
     GMP_LOG("ChromiumCDMChild::OnResolveNewSessionPromise(pid=%u, sid=%s) "
             "resolving %s load session ",
             aPromiseId,
diff --git a/toolkit/components/places/nsNavHistory.cpp b/toolkit/components/places/nsNavHistory.cpp
index 4e52752529fa..0b01d904b2f7 100644
--- a/toolkit/components/places/nsNavHistory.cpp
+++ b/toolkit/components/places/nsNavHistory.cpp
@@ -1939,7 +1939,7 @@ PlacesSQLQueryBuilder::Where()
 
   // If we used WHERE already, we inject the conditions
   // in place of {ADDITIONAL_CONDITIONS}
-  if (mQueryString.Find("{ADDITIONAL_CONDITIONS}", 0) != kNotFound) {
+  if (mQueryString.Find("{ADDITIONAL_CONDITIONS}") != kNotFound) {
     nsAutoCString innerCondition;
     // If we have condition AND it
     if (!mConditions.IsEmpty()) {
diff --git a/toolkit/components/url-classifier/Classifier.cpp b/toolkit/components/url-classifier/Classifier.cpp
index 500780150a91..68169925d2d0 100644
--- a/toolkit/components/url-classifier/Classifier.cpp
+++ b/toolkit/components/url-classifier/Classifier.cpp
@@ -992,7 +992,7 @@ Classifier::ScanStoreDir(nsIFile* aDirectory, nsTArray<nsCString>& aTables)
     // Both v2 and v4 contain .pset file
     nsCString suffix(NS_LITERAL_CSTRING(".pset"));
 
-    int32_t dot = leafName.RFind(suffix, 0);
+    int32_t dot = leafName.RFind(suffix);
     if (dot != -1) {
       leafName.Cut(dot, suffix.Length());
       aTables.AppendElement(leafName);
@@ -1582,7 +1582,7 @@ Classifier::LoadMetadata(nsIFile* aDirectory, nsACString& aResult)
     rv = file->GetNativeLeafName(tableName);
     NS_ENSURE_SUCCESS(rv, rv);
 
-    int32_t dot = tableName.RFind(METADATA_SUFFIX, 0);
+    int32_t dot = tableName.RFind(METADATA_SUFFIX);
     if (dot == -1) {
       continue;
     }