After upgrading to FF5 or FF6 from 3.6.20, I can no longer open links in my work's ticketing site

Question

I work with a State of Alaska web based ticketing system called Unicenter Service Desk, Plus. I had to downgrade back to 3.6.20 from version 5 and again from version 6, because neither of these versions work with this site correctly. Several of the links open new windows from the main window in version 3.6.20, but there is no way to open these windows (even with pop-ups & plugins disabled, all security turned off, all java/JS/etc. enabled) in version 5 or 6.
Other co-workers have also tried upgrading to v.5 and v.6 and have met with the same issue. The downside is that the site is internal (behind a firewall) and secured by username and password, which makes it difficult for you to see what I'm talking about. You may be able to make some sort of troubleshooting access arrangements if you work through the State of Alaska, Department of Administration, Enterprise Technology Services, Help Center at 907-465-1818 (or 1-888-565-8680 Option #4:Computer & Mainframe Support), or by email: [email protected] You may need to ask to speak with Ed Maki as he is one of the chief people who administers the USD system for the State of Alaska.
Unity Service Desk, Plus Product info:
Version: t11US17
This product is licensed to: STATEOFALASKA
SITE ID: 0000032201
Technical Support
Contact Technical Support
for assistance at http://ca.com/supportconnect.
For telephone assistance,
call 800-645-3042 (U.S. and Canada)
or (1) 631-342-4683 (International).

Answer 1

Thanks for the reply. It doesn't have to process the php, it just has to show the HTML content. It did that just fine before the last upgrade but won't now.
I've seen that page you referenced: http://kb.mozillazine.org/File_types_and_download_actions.
It doesn't help. The things it says to look for aren't there for me, specifically:
browser.download.pluginOverrideTypes
plugin.disable_full_page_plugin_for_types
I followed the rest of the instructions but it didn't help.
I did get it to quit opening tabs, instead it prompts me what it should do with the file every time now. What it should do, and used to do, is open the php page and display the HTML content.
Any other ideas?