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".

Reg reader Chris discovered the feature after opening a new tab only to be "greeted by my earlier online banking and webmail sessions complete with account numbers, balances, subject lines etc.

"This content is behind a secure login for a reason," Chris added.

In response to queries on the matter prompted by Chris's experience, 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.

We are aware of the concern and have a fix that will be released in a future version of Firefox. Mozilla remains resolute in its commitment to privacy and user control. The new tab thumbnail feature within Firefox does not transmit nor store personal information outside the user's direct control. The new tab thumbnails are based on users' browsing history. All information is contained within the browser and can be deleted at any time. Users can also switch back to using blank new tab screens by clicking the square icon in the top right corner of the browser. That will change the default preference to show a blank page, rather than the most visited websites when a new tab is opened. Users who share their computer or use Firefox on a public computer should follow best practices for protecting their privacy by utilizing the built-in privacy tools in in Firefox, such as Private Browsing Mode.

Firefox 13 was released on 5 June, adding new features including updated new tab and home tab pages. The updated new tab page feature is broadly akin to the Speed Dial feature already present in other browsers and displays cached copies of a user's most visited websites. ®