Steps to get Posterous Bookmarklet working with Firefox NoScript add-on and 3rd party cookies disabled.

XSS

1. Open the NoScript preferences in Friefox: Tools > Add-ons > NoScript > Preferences
2.  Navigate to the Anti-XSS Protection Exceptions: Advance > XSS
3. Append the following regular expression in the text area: ^http://(?:\w+\.)*posterous\.com

Cookies

1. Open the cookie exceptions on Firefox: Preferences > Privacy > Exceptions
   
2. Then add posterous.com to the text box and click allow