this seems an odd problem, we installed zimbra 5 (open source version) on Ubuntu 6.06 server lts. All is working fine except for the "help" link on the web client.
Now the help works in IE 7 but not in FF2 or Safari. The web mail works fine in both.
Is there any specific setting that needs to be enabled for it?
I presume its something to do with the Java script?