After upgrading to PHP 5.4.28, Magento Connect Downloader is broken. The iframe downloader won't work. Screenshot below. Disabling php-fpm gzip compression allows Magento Connect Downloader to work normally.
Isn't the php-fpm gzip compression extension needed by Magento? How can this be fixed correctly?
UPDATE: Tried on PHP 5.5 with fresh Magento install. The issue persists.