userChrome.css for Firefox, modified version of this -> http://twily.info/firefox/firefox-css

userChrome.css

@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);
/*
Firefox CSS for Nightly/Australis by Twily
** REQUIRES FIREFOX NIGHTLY v29 AND UP
*/
 
:root {
/* VARIABLES */
var-bg-light: #424242; var-bg-dark: #000000;
var-fg-light: #ffffff; var-fg-dark: #ffffff;
var-tab-height: 20px; var-tab-triangle-correction: -1px; var-tab-strip-margin: -23px;
var-tab-fonts: "Lemon",monospace,"Source Code Pro"; var-tab-font-size: 8pt;
}
 
 
@-moz-document url(chrome://browser/content/browser.xul) {
/* TABS */
.tabbrowser-tab[fadein]:not([pinned]) { min-width: 30px !important; max-width: 100% !important; }
tab {
font-family: var(tab-fonts) !important;
min-height: var(tab-height) !important; height: var(tab-height) !important;
background: var(bg-dark) !important; color: var(fg-dark) !important;
font-size: var(tab-font-size); text-shadow: none !important; text-align: center !important;
}
 
.tabbrowser-tab label { padding: 0 calc(var(tab-height)/1) 0 calc(var(tab-height)/1) !important; }
.tabs-newtab-button, .tab-close-button, .tab-close, .tab-throbber, .tab-icon-image, .tab-background-start, .tab-background-end { display: none !important; }
#nav-bar { width: 0 !important; height: 0 !important; overflow: hidden !important; position: fixed !important; margin-left: -1px !important; visibility: hidden !important; }
.tabbrowser-tab *, .tabs-newtab-button * {
background: url(none) !important; list-style-image: none !important;
margin: 0 0 0 0 !important; padding: 0 0 0 0 !important; -moz-appearance: none !important;
}
 
.tabbrowser-tab[selected="true"] .tab-stack {
background: var(bg-light) !important; color: var(fg-light) !important;
border-radius: 0px !important; position: relative !important;
}
.tabbrowser-tab[selected="true"]:before { /* Left Triangle (of selected tab) */
content: '' !important; position: absolute !important; z-index: 2 !important;
top: 0 !important; left: 0 !important; width: 0 !important; height: 0 !important;
border: none !important; border-left: calc(var(tab-height)/2) solid var(bg-dark) !important;
border-top: calc((var(tab-height)/2) - var(tab-triangle-correction)) solid var(bg-light) !important; border-bottom: calc((var(tab-height)/2) + var(tab-triangle-correction)) solid
var(bg-light) !important;
}
.tabbrowser-tab[selected="true"]:after { /* Right Triangle (of selected tab) */
content: '' !important; position: absolute !important; z-index: 2 !important;
top: 0 !important; right: 0 !important; width: 0 !important; height: 0 !important;
border: none !important; border-right: calc(var(tab-height)/2) solid var(bg-dark) !important;
border-top: calc((var(tab-height)/2) - var(tab-triangle-correction)) solid var(bg-light) !important; border-bottom: calc((var(tab-height)/2) + var(tab-triangle-correction)) solid
var(bg-light) !important;
}
 
#TabsToolbar {
height: var(tab-height) !important; min-height: var(tab-height) !important;
-moz-appearance: none !important;
margin-left: var(tab-strip-margin) !important; margin-right: var(tab-strip-margin) !important;
background: var(bg-dark) !important;
}
#TabsToolbar::after { display: none !important; }
.tabbrowser-tab::before, .tabbrowser-tab::after { background: url(none) !important; }
#navigator-toolbox { border: 0 !important; margin-bottom: -1px !important; }
/* MENUS */
menubar, menubutton, menulist, menu, menuitem { font-family: var(tab-fonts) !important; font-size: var(tab-font-size); height: var(tab-height) !important; }
/*#main-menubar, #toolbar-menubar { height: var(tab-height) !important; min-height: var(tab-height) !important; }*/
menuitem + menuseparator, menu + menuseparator { display: none !important; }
.menu-iconic-left { display: none !important; }
menuitem > label { margin-left: var(tab-height) !important; }
 
/* HIDE ORANGE MENU BUTTON */
#appmenu-toolbar-button, #appmenu-button-container { display: none !important; }
/* HIDE STATUS BAR */
#status-bar, #statusbar-display, statuspanel { display: none !important; }
 
/* PRIVATE BROWSING FIX */
#main-window[privatebrowsingmode=temporary] #TabsToolbar::before { display: none !important; }
}
 
 
/* AGENT_SHEET */
@-moz-document url-prefix(http://), url-prefix(https://) {
/* HIDE SCROLLBARD */
scrollbar * scrollbar scrollbarbutton { display: none ! important; }
scrollbar scrollbarbutton { visibility: collapse !important }
 
scrollbar[orient="vertical"], scrollbar thumb[orient="vertical"],
scrollbar[orient="horizontal"], scrollbar thumb[orient="horizontal"] {
display: none !important;
}
 
scrollcorner{opacity: 0 !important;}
}