--- pbtweet_stable.user.js.orig	2009-12-01 14:12:01.000000000 +0900
+++ pbtweet_stable.user.js	2009-12-01 14:10:53.000000000 +0900
@@ -2086,7 +2086,12 @@
 {
 	var insert_HTML = '';
 	var get_url = '';
-	var oLength = document.styleSheets[0].cssRules.length;
+
+	if (document.styleSheets[0].cssRules == null) {
+		var oLength = 0;
+	} else {
+		var oLength = document.styleSheets[0].cssRules.length;
+	}
 	document.styleSheets[0].insertRule('div.conv_chain {clear:both; text-align:left;margin: 5px 5px 4px 0px; padding:0px 0px 0px 0px;}',oLength);
 	document.styleSheets[0].insertRule('div.conv_chain div.thumb{width: 34px !important; height: 34px !important; position:relative !important;max-width:100px;}',oLength+1);
 	document.styleSheets[0].insertRule('div.conv_chain div.thumb img{vertical-align:top; margin-right:4px !important;width:60px !important;max-width:60px !important;height:32px !important;}',oLength+2);