Mozilla Messaging has released the first alpha for the next generation of Thunderbird. Miramar is the code name for the new Thunderbird 3.3 which is built on the new Gecko 2 engine. New in this release: New Addons Manager and extension management API (user interface will be changed before final release). Attachment sizes now displayed along with attachments. Several user interface fixes for Windows Vista/Windows 7. Support for Mac 32/64 bit Universal builds (Miramar Alpha 1 will no longer support PowerPC on Mac). Over 190 platform fixes to improve performance and stability. For more details see the Release Notes. <a…