Be careful with old versions!
These versions are displayed for reference and testing purposes. You should always use the latest version of an add-on.
The most notable changes compared to 2.0 Beta 2 are support for customizable mail compose toolbars and consistent height of mail tabs.
See also http://home.kairo.at/blog/2009-03/earlyblue_and_lcarstrek_for_seamonkey_2