diff --git a/toolkit/components/places/src/Helpers.cpp b/toolkit/components/places/src/Helpers.cpp
index d7ac146b1a0..229f1db7bbb 100644
--- a/toolkit/components/places/src/Helpers.cpp
+++ b/toolkit/components/places/src/Helpers.cpp
@@ -38,9 +38,14 @@
 
 #include "Helpers.h"
 #include "mozIStorageError.h"
+#include "nsIRandomGenerator.h"
+#include "plbase64.h"
 #include "nsString.h"
 #include "nsNavHistory.h"
 
+// The length of guids that are used by history and bookmarks.
+#define GUID_LENGTH 12
+
 namespace mozilla {
 namespace places {
 
@@ -228,5 +233,54 @@ ReverseString(const nsString& aInput, nsString& aReversed)
   }
 }
 
+static
+nsresult
+Base64urlEncode(const PRUint8* aBytes,
+                PRUint32 aNumBytes,
+                nsCString& _result)
+{
+  // SetLength does not set aside space for NULL termination.  PL_Base64Encode
+  // will not NULL terminate, however, nsCStrings must be NULL terminated.  As a
+  // result, we set the capacity to be one greater than what we need, and the
+  // length to our desired length.
+  PRUint32 length = (aNumBytes + 2) / 3 * 4; // +2 due to integer math.
+  NS_ENSURE_TRUE(_result.SetCapacity(length + 1), NS_ERROR_OUT_OF_MEMORY);
+  _result.SetLength(length);
+  (void)PL_Base64Encode(reinterpret_cast<const char*>(aBytes), aNumBytes,
+                        _result.BeginWriting());
+
+  // base64url encoding is defined in RFC 4648.  It replaces the last two
+  // alphabet characters of base64 encoding with '-' and '_' respectively.
+  _result.ReplaceChar('+', '-');
+  _result.ReplaceChar('/', '_');
+  return NS_OK;
+}
+
+nsresult
+GenerateGUID(nsCString& _guid)
+{
+  _guid.Truncate();
+
+  // Request raw random bytes and base64url encode them.  For each set of three
+  // bytes, we get one character.
+  const PRUint32 kRequiredBytesLength =
+    static_cast<PRUint32>(GUID_LENGTH / 4 * 3);
+
+  nsCOMPtr<nsIRandomGenerator> rg =
+    do_GetService("@mozilla.org/security/random-generator;1");
+  NS_ENSURE_STATE(rg);
+
+  PRUint8* buffer;
+  nsresult rv = rg->GenerateRandomBytes(kRequiredBytesLength, &buffer);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = Base64urlEncode(buffer, kRequiredBytesLength, _guid);
+  NS_Free(buffer);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  NS_ASSERTION(_guid.Length() == GUID_LENGTH, "GUID is not the right size!");
+  return NS_OK;
+}
+
 } // namespace places
 } // namespace mozilla
diff --git a/toolkit/components/places/src/Helpers.h b/toolkit/components/places/src/Helpers.h
index d7d7a2aa448..29efd3df99e 100644
--- a/toolkit/components/places/src/Helpers.h
+++ b/toolkit/components/places/src/Helpers.h
@@ -200,6 +200,13 @@ void GetReversedHostname(const nsString& aForward, nsString& aRevHost);
  */
 void ReverseString(const nsString& aInput, nsString& aReversed);
 
+/**
+ * Generates an 12 character guid to be used by bookmark and history entries.
+ *
+ * @note This guid uses the characters a-z, A-Z, 0-9, '-', and '_'.
+ */
+nsresult GenerateGUID(nsCString& _guid);
+
 /**
  * Used to finalize a statementCache on a specified thread.
  */