Firefox 3 is not fully supported by Blackboard at this time. You may receive reports from students that when they turn in an assignment they get an error message. You can suggest that your students use Internet Explorer 7 or Firefox 2 instead. In fact, that's a good suggestion whenever a student has problems with an assignment or test, to tell them to try using a different browser. Each browser has its little quirks and even though Blackboard tries very hard to work around those, sometimes it's just easier to try a different browser.
Here's Blackboard's browser information page. Choose the "Vista 8.0 and Campus Edition 8.0" option.