Privacy-conscious users have sounded the alarm after it emerged the "New Tab" thumbnail feature in Firefox 13 is "taking snapshots of the user's HTTPS session content".
Mozilla acknowledged that the behaviour was undesirable and promised a patch. In the meantime, the browser and email client firm points privacy-conscious users towards various workarounds, as a statement (below) explains. [more]
To disable this goto ABOUT:CONFIG and change the following to false
Usually they arent that careless!!! (Thier spying cant be detected by end users)