I think what we are supposed to understand is that this Firefox Hamburger Menu (FHM) is really a TOA: Toolbar Overflow Area. It's a repository of icons for doing arbitrary things.
Its Customize button at the bottom invokes exactly the same UI as View/Toolbars/Customize: a big view where you can move icons between an editable version of the FHM, the browser toolbar, and a repository of available tools (shown in the main pane as a large area).
So any item that can be on your toolbar can go into FHM, including bookmarks. Hence: TOA: toobar overflow area for items you don't use much.
It would be better if they initialized it empty, and if it somehow clearly communicated "Hey, I am a toolbar overflow area: put stuff here that would go on the toolbar that you don't need so much, when you don't have space on the toolbar."
A hamburger on its own is, like the article says, dead weight with no meaning. If its on a bar with a bunch of other nav options and you feel like the one you want is missing you often use it.
If I ever get around to it I'll hack up the bootstrap code and make it tab based (icon + text underneath) but that seems like a PITA with how bootstrap does its layouts in nav bars from my paltry experience.