Firefox 3 has implemented some new cookie settings. If you don't have the settings configured correctly, Facebook will not load through the Tracker. This is how to configure the settings:

On a Windows machine, in Firefox, click Tools, then Options. In the Options window, click on the Privacy icon.
On a Mac machine, in Firefox, click Firefox, then Preferences. In the window that appears, click on the Privacy icon.

Most likely, Accept third-party cookies will be unchecked. I suggest this. Clicking this option will make the Tracker work, but it may allow malicious websites to place cookies you do not want on your system. Instead, click Exceptions. (See Fig. 1)

Figure 1

Enter the four domains Firefox uses on a regular basis to operate, clicking Allow after each entry. (See Fig. 2)

Figure 2

That's it! After saving these settings, Facebook will work properly through the Tracker in Firefox 3.