It's not a session timeout. They were actively using ZCS. Jetty access log shows a request for loginOp=logout.
Coincidences: upgrade from 6.0.9 to 6.0.12p1; all users running MacOS; all users running Firefox 4.0 or 4.0.1. No unusual FF extensions.
Anyone else seeing this, or have troubleshooting suggestions?
*.*.*.* - - [19/Apr/2011:14:19:52 +0000] "GET /zimbra?loginOp=logout HTTP/1.1" 302 0 https://mail.example.com/zimbra/" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.5; rv:2.0.1) Gecko/20100101 Firefox/4.0.1"