I, unfortunately, don’t have direct use of any Apple hardware, so it’s hard for me to troubleshoot without being able to get my hands dirty, as it were. But I have heard one or two reports of instructors not being able to scroll right-to-left in the Blackboard Grade Center while using Firefox for Mac.
Psychology instructor Ryan Newton came up with a solution — after some searching, he found that these instructions from the University of Oregon library system’s website seem to do the trick. It looks like Mac users may just have to ensure that their Firefox installations are always showing scrollbars. Here’s another guide to the settings change.