Does your Concourse page look like this in Firefox?
This is a rendering error in Firefox which appears only on the Teach tab and is annoying but fixable. It results from a tool’s broken link to its icon. While the problem with the broken icon link on the server has been fixed, for this semester only coursesites still displaying the problem must be fixed individually.
Here’s what you do inside your course. From the Build tab, Manage Course > Course Menu > ND Library (title may repeat) > Click the grey square next to that title > Choose Delete from the drop down menu.