How to remove top menu on sidebar

[BPUPH]

I am wondering if there is a way to remove this top menu from the sidebar:

It gets in the way when it comes to dragging tabs onto other tabs. I don't remember it being there in a previous version I used. I just had to reinstall Firefox and I can't find any option to disable it.

[irvinm]

userChrome.css:

#sidebar-header { display: none; }

I think this should work, but I did not try. (This is a Firefox\Sidebar change ... nothing to do with TST)