At present you are unable to see Trusted Sites using Firefox. Mozilla is aware of the issue and they will hopefully have a solution in the next release of Firefox.
Firefox Add-Ons
Try installing a compatibility add-on in your Firefox. It is not guaranteed that these will work, but they will allow you greater access to the Online Curriculum Organsier. The following Add-Ons enable you to display pages in 'Internet Explorer mode' using Firefox:
1. IE Tab
2. IE View
* Please note that we are not affiliated with the Add-Ons or their Developers in any way, so please refer to the Developer's website if you have any trouble with the extension.
Using Bootcamp, VMWare Fusion or Parallels Desktop
One short term fix would be to use BootCamp- you can reboot your Mac in to Windows XP (SP2) if you've got a disc or even better use a program like VMWare Fusion or Parallels Desktop where you can have both Windows XP and Mac OS running on the same screen.