Зашёл на http://www.seamonkey-project.org/releases/, а там:
•If you are using NoScript you might encounter a certificate error when trying to download SeaMonkey from this site. NoScript tries to force an https connection for an http only site. It is not a NoScript problem but how the Mozilla server, from which downloads are delivered, is configured.
In this case please add download.cdn.mozilla.net to the NoScript «Never force secure (HTTPS) connections» options or turn off NoScript for this download only. The settings are located in the NoScript options under «Advanced->HTTPS».
А я давно говорил что мода на повальное шифрование всего и вся среди вебмакак и прочих неосиляторов ничем хорошим не кончится, теперь вот и браузер без пердолинга не скачаешь.