Great extension, but having the same issues as danermo and Alexey in FF50 (Win10). If I have a button with a pull-down button, the bookmark icons disappear. In my case, the pull down button is the "Display closed tabs" button from Tabs Mix Plus. Remove that button from the vertical toolbar, and it works fine.
The issue is only when I choose "Show: Icons" under the Buttons options. "Icons and Text" and "Text" options both work fine.
FWIW, the bookmark buttons do not work; however, I can right-click and choose "Open All..."