Gflash updated to version 1.4.11
(as much as I love how it looks, it's creating waaaaay too many problems on client&server, let's just forget about it for now)
Type in the modpack name (Gflash) or paste the following url into the search box.
Finally, click Install at the bottom right of the launcher after you select Gflash from the list on the left. The launcher will handle everything else!