Mozilla Connect

Apparently, using userChrome.css my problem is solvedsidebar-main{  display: none !important;}

Indeed, it makes sense to add a toolbar of 2px so the window can easily be dragged.

I can't hide the small sidebar (=native vertical tabs), while also hiding the horizontal tabs. That was what I was trying to say. 

I really would like the ability to hide the vertical tabs. I enabled vertical tabs because then the horizontal tabs disappear, but I want to use my custom vertical tabs extension (for example Tab Center Reborn). Having vertical tabs twice is overkill...