In addition to my post (link here) I've noted that sometimes isn't possible to start the Zimbra Desktop. I've tried to start it from the terminal ./zdesktop but I get a error message:
Apparently this problem is due to prisma (an application that lets users split web applications out of their browser and run them directly on their desktop - link)Couldn't load XPCOM.
So, finding the source of this problem I've tried to install prisma but I got the same error message (Couldn't load XPCOM.)
The solution: Install through yum 'xulrunner' of your OS version. In order to search your version run the following command: 'yum search mozilla'. Then, install the most appropriate XUL Runtime for Gecko Applications's plugin.