"incompatible with semonkey 2.15" Rated 1 out of 5 stars

lightning is a featured extension with mozilla's brand on it. A calendar is pretty important in a clients like these -- and yet this one is not properly updated for seamonkey -- making this extension, and seamonkey unreliable as PIM.

This review is for a previous version of the add-on (1.9). 

I will be discussing this with the Seamonkey folks, but really this is a hard call. If I would have uploaded a compatible version for Seamonkey, then Thunderbird users would have complained that the latest version of Lightning is not compatible to the latest version of Thunderbird. As you've noted, vice versa for Seamonkey.

Just dumping in the binary component to support both versions at a time is also not very productive, since it creates a mess regarding support (we need to know the exact Lightning and Thunderbird/Seamonkey version) as well as with code quality (we need to add more and more blocks with if (thunderbird 17 and lightning 1.9) { ... } else if (seamonkey 2.15 and lightning 2.0) { ... } ).

Also this makes it even harder for QA. The Lightning Project is mostly a community project, there is no staff paid by Mozilla. If we support both Thunderbird 17 and Seamonkey 2.15 (which use two totally different versions of the Mozilla Platform), this means yet another platform that needs to be tested.

There are some proposed solutions, but this needs to be discussed with the Seamonkey Council first, which won't happen before the end of the month.

I will blog about this with more details soon, see blog.mozilla.org/calendar

In the meanwhile, please use the development channel builds, 2.0b1