After nearly a year in development, Mozilla/Mozilla Labs has released Thunderbird 5.0 on June 28th. As mentioned prior to keep the version numbering the same across all products, there was not a Thunderbird 4.0 release. Further during early development this was labeled as Thunderbird 3.3 Alpha. Users who’s computers meet these system requirements should be prompted to update with in 24-48 hours or Windows user can go to Help > Check For Updates… and should be presented with an update offer (see below). Please note, some add-ons may not yet be working with Thunderbird 5.0. See this post for more information and options. See What’s New in Thunderbird 5.0.