Fixing tests to pass on Firefox. Apparently if you have <link> to a

stylesheet but the href attribute is missing or the stylesheet can't be
found, the <link> can NOT be disabled and its .disabled property will
ALWAYS return false.

tests/tests.js

@@ -2,27 +2,29 @@
 var testHeadHtml = (
 	// Not in groups
 	'<style id="lone-style"></style>' +
-	'<link id="lone-link" rel="stylesheet">' +
+	'<link id="lone-link" rel="stylesheet" href="tests.css">' +
 
 	// Not stylesheets
 	'<link id="icon-link" rel="icon" title="Icon" class="group-a group-b group-c">' +
 	'<meta id="meta-element" class="group-a group-b group-c">' +
 
 	// Group of standard links
-	'<link id="standard-link" rel="stylesheet" title="Default">' +
-	'<link id="alternate-link" rel="alternate stylesheet" title="Alternate">' +
+	// Note: On Firefox links to inexistent stylesheets can NOT be disabled and
+	// their .disabled property always returns false.
+	'<link id="standard-link" rel="stylesheet" title="Default" href="tests.css">' +
+	'<link id="alternate-link" rel="alternate stylesheet" title="Alternate" href="tests.css">' +
 
 	// Group of styles
 	'<style id="style-a-1" class="group-a 1"></style>' + 
 	'<style id="style-a-2" class="group-a 2"></style>' +
 
 	// Mixed group
 	'<style id="style-b-1" class="group-b 1"></style>' + 
-	'<link id="link-b-2" class="group-b 2" rel="stylesheet">' + 
+	'<link id="link-b-2" class="group-b 2" rel="stylesheet" href="tests.css">' + 
 
 	// Group of two non-standard links
-	'<link id="link-c-1" class="group-c 1" rel="stylesheet">' + 
-	'<link id="link-c-2" class="group-c 2" rel="stylesheet">'
+	'<link id="link-c-1" class="group-c 1" rel="stylesheet" href="tests.css">' + 
+	'<link id="link-c-2" class="group-c 2" rel="stylesheet" href="tests.css">'
 );
 
 QUnit.test("Export test", function( assert ) {