I have a working installation of Z6.0.2 since several times, no problems of sort.

Since few days, I only have problems opening the contact tab in firefox, while it works with Chrome.
Debugging with Firebug, I got this:
uncaught exception: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIXMLHttpRequest.send]" nsresult: "0x80004005 (NS_ERROR_FAILURE)" location: "JS frame :: https://myserverhost/zimbra/ :: anonymous :: line 647" data: no]
10 active mailbox, different users, I am the only one experiencing these problems.