A Kindle firmware update, due to be rolled out to all users in May, will allow owners to share their favourite passages from ebooks on Facebook and Twitter.

The social networking-friendly patch will also improve PDF viewing, with new zoom and pan functionality. And, the ability to collate books and documents into collections will be added to the menu system.

Two new fonts will be available, and users will be able to password protect their Kindle or Kindle DX.

The 2.5 patch has been on limited trial with a number of existing owners, but is now considered stable enough for general release.