Do you mean Veritas Cluster Server? Perhaps you could use a Microsoft browser for that so you don't have to install an unsafe version of Firefox. Or do you mean the software is so out of date that NO browser except Firefox through version 23 will work with it? (In that case, shame on Symantec.)

Use the Firefox Portable 23.0.1 version for just that website: http://sourceforge.net/projects/portableapps/files/Mozilla%20Firefox,%20Portable%20Ed./Mozilla%20Firefox,%20Portable%20Edition%2023.0.1/

It will install separately from any other version of Firefox that you may have installed.

Do you know what changes in more recent Firefox versions caused it to stop working?

Cor-el,

Not sure about why newer versions won't work. I've been told twice by our IT help desk that I need to uninstall newer version and download 23. They have indicated that it will not work with later versions. That is true as I no longer can access my desktop using Citrix Receiver. They have also instructed me to be certain to go to the settings and not search for future updates as the same problem will occur. Is there somewhere where I can access the version 23 download, hopefully with instructions.

First, Citrix Receiver is a different issue. Could you look at this post from the Firefox 30 days: https://support.mozilla.org/questions/1010038#answer-601964

Second, I suggest using the Portable build that the-edmeister linked to, just for VCS. For normal web browsing, you can close that and use Firefox 40.