One of the goals for Thunderbird 3 is to be a much better platform for which to develop add-ons.
We’re planning and doing some in-product and in-codebase work to that end, including documenting APIs (shocking, I know), bundling STEEL, which should make it easy to do 80% of what add-on authors want to do without resorting [...]

PC World’ s editors have selected Mozilla Thunderbird as one of “The 100 Best Products of 2008 Award” winners, specifically in the 43rd position, in between the Rock Band controllers and the Dell XPS 420 (???).
That’s a weird and fascinating list. I’m not a huge fan of this kind of list in general. [...]