Mozilla has announced yesterday that it will start rolling out silent updates to Firefox beginning in June.
Robert Nyman, Mozilla technical Evangelist listed silent updates as one of the projects the company will finish this year in a blog post summarizing Mozilla's 2011's accomplishments on Wednesday.
Silent updates will arrive in the form of Firefox 13. Mozilla have apparently been working on silent updating for about 17 months and had originally thought they could add the feature to Firefox 4,
Source : Here