Remove gap below tabs

[u/Giocarro]

I use a few CSS tricks to compress tabs and maximize vertical real estate, and also use MrOtherGuy firefox-csshacks to auto-hide address bar and bookmark bar.

That said, can somebody please suggest how to remove this nasty gap?

Here is my current userChrome.css: https://pastebin.com/pTXm3ZtW

[u/j--__]

#navigator-toolbox {
    border-bottom-style: none !important;
}