Creating auto-updating option for extensions in Firefox, Safari, and Chrome

Creating auto-updating option for extensions in Firefox, Safari, and Chrome We have already got our extensions for Firefox, Chrome and Safari. We now want to incorporate auto-update option for extensions. Whenever we have a new version of extension available, browser should prompt users with existing extension -- Do you want to update extension? When user clicks yes, it should update the extension to new version. Please let me know how much would you charge to implement this?