based on devedition dark theme (enable the theme first) with slightly tweak.

userChrome.css

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

/* Hidden */
#titlebar-max,#titlebar-close,#titlebar-min,.titlebar-placeholder, /* Winblows 10 stuff */
#sidebar-search-container,#sidebar-header,
.toolbarbutton-menu-dropmarker,.toolbarbutton-menubutton-dropmarker,
.tabbrowser-arrowscrollbox > .scrollbutton-up,.tabbrowser-arrowscrollbox > .scrollbutton-down,
#context-sharelink,#context-savelink,#lpt_lpfillformsmenu4,#context-sendimage,#context-setDesktopBackground,#context_toggleMuteTab,
.tab-close-button,#alltabs-button { display: none !important; }

:root[devtoolstheme="dark"] { 
    --chrome-secondary-background-color: #2b2633 !important;
    --chrome-selection-background-color: #6c6181 !important;
}

/* Tabs */
.tabbrowser-tabs:not([drag=detach]) > .tabbrowser-tab:not([pinned])[fadein] {
    min-width: 30px !important;
    max-width: 250px !important;
}

#main-window[sizemode="maximized"] .tabbrowser-arrowscrollbox > .arrowscrollbox-scrollbox,
#main-window[sizemode="normal"] .tabbrowser-arrowscrollbox > .arrowscrollbox-scrollbox {
    padding-left: 0px !important;
    padding-right: 0px !important;
}

.tabbrowser-tabs {
    text-align: center !important;
    text-shadow: 0.01em 0.01em 0.01em #777;
    font-size: 13px !important;
    max-height: 15px !important;
    min-height: 15px !important;
    color: #948d8d !important;
    --tab-hover-background-color: none;
    --tab-selection-background-color: #1a1a1f; /* #2b2633*/
    --tab-selection-color: #c8c7d6;
    --tab-selection-box-shadow: 0 1px 0 #9f8ba9 inset;
    --pinned-tab-glow: radial-gradient(75px at center calc(100% - 2px), rgba(184,46,229,0.9) 14%, rgba(0,0,0,0.4) 18%, transparent 70%);
}

.tabbrowser-tab[pinned] { box-shadow: 0 2px 0 #e5527f inset; }
.tabbrowser-tab .tab-text:not([pinned]) { margin-top: -18px !important; }
.tab-icon-sound { margin-top: -18px !important; }
.tab-icon-image,.tab-throbber,.tab-throbber[progress] {
    margin-top: -16px !important;
    max-width: 11px !important;
    max-height: 11px !important;
}

/* Winblows 10 stuff; Titlebar */
#main-window[sizemode="normal"] > #titlebar { -moz-appearance: none !important; }
#main-window[sizemode="maximized"] > #titlebar { margin-top: -5px !important; }
#urlbar { text-shadow: 0.01em 0.01em 0.01em #999; }

/* Vimpr statusline */
#liberator-status-input,
#liberator-status-bookmark,
#liberator-status-history { color: #ff4081; }
/* #liberator-status-tabcount,
#liberator-status-position { color: #f2f2f2; } */
/* Fix Vimpr on Winblows with a stupid bottom line 
#browser-bottombox,#liberator-separator { display: none !important; } */

label.statuspanel-label {
    font-family: Monospace !important;
    font-size: 14px !important;
    padding-top: 0 !important;
    padding-bottom: 0 !important;
    border: 0 !important;
    color: #9d9c95 !important;
    background-image: none !important;
    background-color: #1a1a1f !important;
}

statuspanel[type=overLink], statuspanel[inactive][previoustype=overLink] {
    -moz-transition: none !important; }

/* Tab numbers 41+ */
tab { counter-increment:tabnumber; }
.tabbrowser-tabs .tabbrowser-tab:after {
    margin-left: -15px !important;
    margin-top: 0px !important;
    width: 15px !important;
    font-family: monospace !important;
    font-size: 13px !important;
    content: counter(tabnumber) !important;
    position: absolute !important;
    background: none !important;
    color: #d8d6dc !important;
    opacity: 0.9 !important;
}

.tabbrowser-tabs .tabbrowser-tab[selected]:after {
    font-weight: bold !important;
    color: #eed7ff !important;
    opacity: 1 !important;
}