If you open multiple fonts in the font viewer, the action buttons in the toolbar of the application are presented one for each font file opened.

For example, if you select three fonts in "Files" and open with Font Viewer, you get three "back arrows" on the left of the toolbar, and three "info" and "install" buttons. (see attached screenshot with Font Viewer in the foreground, and nautilus in the background)


This bug also presents if you open a font, keep font viewer open, go back to Files, and open another. The more you open, the more buttons that appear.