As far I as can see the Firefox's Bookmark button will show up if you have the Menu b
Sou you can try the following.
Disable the global menu and Hide the Menu Bar to enable the button.
1) Open Firefox and type about:config in the address bar, then click to confirm in "I'll be careful, I promise"
- Search the key "ui.use_unity_menubar" and select it , then double click to change the value from true to false
2) Right click in the firefox window and "uncheck" Menu Bar.
After that you should have the Firefox Button instead the menubar, and the Bookmarks button will appears.
Then Right click and select "Customize.." to drag the Bookmarks button from you Navigation Toolbar to your Bookmarks toolbar.
Finally you can go to "about:config" and enable the "ui.use_unity_menubar" key to display the unity global menu.
Install the following addon named Classic Bookmarks Button.
1) Install the Classic Bookmarks Button and restart Firefox.
2) Right click and select "Customize..".
- Drag the Bookmarks Button to your Navigation or Bookmarks Toolbar.
In Navigation Toolbar:
Or in Bookmarks Toolbar:
Hope it helps!