The Adobe Exchange Download page has an old version of Adobe Extension Manager that fails on Mac OS Mountain Lion and later. Anyone who attempts to download Extension Manager gets this old version, 5.5.0.163.
BAD - http://www.adobe.com/exchange/em_download/em55_download.html
Version 5.5.3 is available from the following link, but Adobe search and download page link to the exchange download, not this link.
Adobe, Please update the link so that we can a little more easily download a version that doesn't show the misleading error "The Extension does not contain a valid signature. The extension will not be installed".