Firefox 57 Interface Tweaks

userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); 

.tab-background {
    background-attachment: none!important;
    background-color: #cccdcf!important;
    background-image: none!important;
}

.tab-background[selected="true"] {
    background-attachment: none!important;
    background-color: #F5F6F7!important;
    background-image: none!important;
}

.tab-line { display: none !important; }

/*
.tabbrowser-arrowscrollbox > .scrollbutton-up, .tabbrowser-arrowscrollbox > .scrollbutton-down {
  display: none;
}
*/

.tabbrowser-tab > .tab-stack > .tab-content[pinned][titlechanged] {
  background-position: center bottom !important;
  background-size: 8px !important;
  background-image: none !important;
  background: -moz-linear-gradient(top, rgba(204,205,207,0) 80%, rgba(68,68,68,0.0) 86%, rgba(68,68,68,1) 95%) !important;
}