diff --git a/xpcom/string/nsReadableUtils.cpp b/xpcom/string/nsReadableUtils.cpp
index 879b4ef5cdb5..d8904fe95c59 100644
--- a/xpcom/string/nsReadableUtils.cpp
+++ b/xpcom/string/nsReadableUtils.cpp
@@ -1026,6 +1026,17 @@ CountCharInReadable(const nsACString& aStr, char aChar)
   return count;
 }
 
+bool
+StringBeginsWith(const nsAString& aSource, const nsAString& aSubstring)
+{
+  nsAString::size_type src_len = aSource.Length(),
+                       sub_len = aSubstring.Length();
+  if (sub_len > src_len) {
+    return false;
+  }
+  return Substring(aSource, 0, sub_len).Equals(aSubstring);
+}
+
 bool
 StringBeginsWith(const nsAString& aSource, const nsAString& aSubstring,
                  const nsStringComparator& aComparator)
@@ -1038,6 +1049,17 @@ StringBeginsWith(const nsAString& aSource, const nsAString& aSubstring,
   return Substring(aSource, 0, sub_len).Equals(aSubstring, aComparator);
 }
 
+bool
+StringBeginsWith(const nsACString& aSource, const nsACString& aSubstring)
+{
+  nsACString::size_type src_len = aSource.Length(),
+                        sub_len = aSubstring.Length();
+  if (sub_len > src_len) {
+    return false;
+  }
+  return Substring(aSource, 0, sub_len).Equals(aSubstring);
+}
+
 bool
 StringBeginsWith(const nsACString& aSource, const nsACString& aSubstring,
                  const nsCStringComparator& aComparator)
@@ -1050,6 +1072,17 @@ StringBeginsWith(const nsACString& aSource, const nsACString& aSubstring,
   return Substring(aSource, 0, sub_len).Equals(aSubstring, aComparator);
 }
 
+bool
+StringEndsWith(const nsAString& aSource, const nsAString& aSubstring)
+{
+  nsAString::size_type src_len = aSource.Length(),
+                       sub_len = aSubstring.Length();
+  if (sub_len > src_len) {
+    return false;
+  }
+  return Substring(aSource, src_len - sub_len, sub_len).Equals(aSubstring);
+}
+
 bool
 StringEndsWith(const nsAString& aSource, const nsAString& aSubstring,
                const nsStringComparator& aComparator)
@@ -1063,6 +1096,17 @@ StringEndsWith(const nsAString& aSource, const nsAString& aSubstring,
                                                                aComparator);
 }
 
+bool
+StringEndsWith(const nsACString& aSource, const nsACString& aSubstring)
+{
+  nsACString::size_type src_len = aSource.Length(),
+                        sub_len = aSubstring.Length();
+  if (sub_len > src_len) {
+    return false;
+  }
+  return Substring(aSource, src_len - sub_len, sub_len).Equals(aSubstring);
+}
+
 bool
 StringEndsWith(const nsACString& aSource, const nsACString& aSubstring,
                const nsCStringComparator& aComparator)
diff --git a/xpcom/string/nsReadableUtils.h b/xpcom/string/nsReadableUtils.h
index 6a697d5eaedc..12b2e67465bf 100644
--- a/xpcom/string/nsReadableUtils.h
+++ b/xpcom/string/nsReadableUtils.h
@@ -386,18 +386,18 @@ uint32_t CountCharInReadable(const nsAString& aStr,
 uint32_t CountCharInReadable(const nsACString& aStr,
                              char aChar);
 
+bool StringBeginsWith(const nsAString& aSource, const nsAString& aSubstring);
 bool StringBeginsWith(const nsAString& aSource, const nsAString& aSubstring,
-                      const nsStringComparator& aComparator =
-                        nsDefaultStringComparator());
+                      const nsStringComparator& aComparator);
+bool StringBeginsWith(const nsACString& aSource, const nsACString& aSubstring);
 bool StringBeginsWith(const nsACString& aSource, const nsACString& aSubstring,
-                      const nsCStringComparator& aComparator =
-                        nsDefaultCStringComparator());
+                      const nsCStringComparator& aComparator);
+bool StringEndsWith(const nsAString& aSource, const nsAString& aSubstring);
 bool StringEndsWith(const nsAString& aSource, const nsAString& aSubstring,
-                    const nsStringComparator& aComparator =
-                      nsDefaultStringComparator());
+                    const nsStringComparator& aComparator);
+bool StringEndsWith(const nsACString& aSource, const nsACString& aSubstring);
 bool StringEndsWith(const nsACString& aSource, const nsACString& aSubstring,
-                    const nsCStringComparator& aComparator =
-                      nsDefaultCStringComparator());
+                    const nsCStringComparator& aComparator);
 
 const nsAFlatString& EmptyString();
 const nsAFlatCString& EmptyCString();