Hide Tab Bar in Firefox 57+

Finally I've found a way to hide tabs from Firefox.
I use Tree Style Tabs addons and don't need native tabs.

So here is how you can do it:

Create a new file in your browsers' profile: ~/.mozilla/firefox/somestring.default/chrome/userChrome.css
and add following content:

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */
/* to hide the native tabs */
#TabsToolbar {
    visibility: collapse;
}

/* to hide the sidebar header */
#sidebar-header {
    visibility: collapse;
}

Restart your browser and enjoy!