Some students and instructors who use Macs find that PDF type documents will not open correctly when they are using recent versions of Safari or Firefox on Macs. Instead, Blackboard gives them an almost-blank window with an error saying that a “plug-in” is missing.
The solution is to download the PDF Browser Plugin from http://www.schubert-it.com, and install it on your Mac. Installation is simple: just doubleclick the downloaded .dmg file, doubleclick "PDF Browser Plugin.mpkg and follow the instructions.
The first time you use it to view a PDF in a browser window you will be asked to provide a license number, but if you select "educational use" then you will be allowed to use the software without paying a license fee.
This plugin is not needed for Chrome, but will work with both Mac Firefox and Safari, and it should allow you to view PDFs in Blackboard.
If you have a PC, use the Adobe Reader plugin instead.
A few Mac users may have Adobe Acrobat installed on their machines. If so, then in addition to installing PDF Browser Plugin, run Firefox and visit Tools > Add-ons. Disable Adobe Acrobat NPAPI Plugin if it is installed, and enable PDF Browser Plugin instead.
Additional information about this plugin (which works for both Safari and Firefox) can be found at http://www.schubert-it.com/pluginpdf/