Thanks for your review. It's currently possible via a hidden option. Export your settings and change the value of "tabMenuEnabled" in the exported file to false (it's set to true by default). Then, you just have to import this modified file and the menu entry should disappear.

Edit:
You're welcome!

Thank you! Now there's also SingleFileZ :)
More info here: https://addons.mozilla.org/firefox/addon/singlefilez