I've encountered this problem many times when working with VMware Server, and it is one of the reasons that I try to avoid Server these days and use ESXi as much as possible. But if you really need server, here are some of the things that I've found help (and I realize that some of them probably won't work for you, or don't apply, because you've already tried them).
Make sure that the correct hostname is in /etc/hosts in Ubuntu for at least the localhost (127.0.0.1) entry.
Try a version of Firefox that was around when Server was last released/updated.
Make sure you installed following the instructions here: https://help.ubuntu.com/community/VMware/Server, including the patches that are listed as one of the steps. Note that the instructions for 10.04 are the same as the 9.10 instructions, and the link to the patches may be out of date (but this one still works for me: http://radu.cotescu.com/how-to-install-vmware-server-ubuntu-fedora-opensuse/).