The behavior of toString() and toSource() on empty regexps has changed. See bug 225550 and bug 226045.

js/tests/ecma_2/RegExp/properties-001.js

@@ -56,8 +56,15 @@ function AddRegExpCases( re, s, g, i, m, l ) {
                  s,
                  re.source );
 
+/*
+ * http://bugzilla.mozilla.org/show_bug.cgi?id=225550 changed
+ * the behavior of toString() and toSource() on empty regexps.
+ * So branch if |s| is the empty string -
+ */
+var S = s? s : '(?:)';
+
     AddTestCase( re + ".toString()",
-                 "/" + s +"/" + (g?"g":"") + (i?"i":"") +(m?"m":""),
+                 "/" + S +"/" + (g?"g":"") + (i?"i":"") +(m?"m":""),
                  re.toString() );
 
     AddTestCase( re + ".global",

js/tests/js1_2/regexp/toString.js

@@ -38,10 +38,13 @@
 	var count = 0;
 	var testcases = new Array();
 
-    // var re = new RegExp(); re.toString()
+    /*
+     * var re = new RegExp(); re.toString()  For what to expect,
+     * see http://bugzilla.mozilla.org/show_bug.cgi?id=225343#c7
+     */
 	var re = new RegExp();
 	testcases[count++] = new TestCase ( SECTION, "var re = new RegExp(); re.toString()",
-	                                    '//', re.toString());
+	                                    '/(?:)/', re.toString());
 
     // re = /.+/; re.toString();
     re = /.+/;