userChrome.css

:root {
    /*--z-color-accent: #F0360D;*/
    --z-color-accent: #E25821;
    --z-color-background-dark: #212121;
    --z-color-background-light: #424242;
}

/* colors */

html#main-window {
    --arrowpanel-background: var(--z-color-background-dark) !important;
    --toolbar-bgcolor: var(--z-color-background-dark) !important;
    --lwt-toolbar-field-background-color: var(--z-color-background-light) !important;
    --lwt-toolbar-field-focus: var(--z-color-background-light) !important;
}

:root:-moz-lwtheme-brighttext {
    --autocomplete-popup-background: var(--z-color-background-dark) !important;
}

tabs#tabbrowser-tabs {
    --tab-line-color: var(--z-color-accent) !important;
    --tab-loading-fill: var(--z-color-accent) !important;
}

#sidebar-box {
    --sidebar-background-color: var(--z-color-background-dark) !important;
}

/* hide elements */

#overflowMenu-customize-button {
    display: none;
}

/* new omnibar */

#urlbar[breakout] {
    width: 100% !important;
    top: calc((var(--urlbar-toolbar-height) - var(--urlbar-height)) / 2) !important;
    left: 0 !important;
}

#urlbar[breakout][breakout-extend] > #urlbar-input-container {
    height: var(--urlbar-height) !important;
    padding-block: 0 !important;
    padding-inline: 0 !important;
}

#urlbar[breakout] > #urlbar-input-container {
    height: var(--urlbar-height) !important;
}

.urlbarView {
    margin-block-start: 0 !important;
}

.urlbarView-results {
    padding-block: 0 4px !important;
}

.urlbarView .urlbarView-row-inner {
    padding-block-start: 3px !important;
    padding-block-end: 6px !important;
}

.urlbarView-row:first-child {
    margin-top: 2px;
}

.urlbarView-row {
    padding-block: 1.5px !important;
}

.urlbarView-row[type="search"]:not([selected]):not(:hover):not([show-action-text]) > .urlbarView-row-inner > .urlbarView-no-wrap > .urlbarView-action {
    display: block !important;
}

.urlbarView-row[type="search"]:not([selected]):not(:hover):not([show-action-text]) > .urlbarView-row-inner > .urlbarView-no-wrap > .urlbarView-title-separator {
    visibility: visible !important;
}

#urlbar:-moz-lwtheme > #urlbar-background, #navigator-toolbox #searchbar:-moz-lwtheme {
    background-color: var(--z-color-background-dark) !important;
}

#urlbar-input-container {
    background-color: var(--lwt-toolbar-field-background-color, hsla(0,0%,100%,.8)) !important;
}

.urlbarView {
    width: 100% !important;
}

.urlbarView .urlbarView-body-inner {
    border-top-color: transparent !important;
}

.urlbarView {
    margin-inline: 0 !important;
}

#urlbar[focused="true"] > #urlbar-input-container {
    border-color: var(--toolbar-field-focus-border-color) !important;
    border-bottom-color: transparent !important;
}

#urlbar[focused="true"]:not([open]) > #urlbar-input-container {
    border-bottom-color: var(--toolbar-field-focus-border-color) !important;
}

#urlbar .search-one-offs:not([hidden]) {
    padding-block: 4px !important;
    margin-bottom: 4px;
}

.urlbarView .urlbarView-row-inner {
    border-radius: 0 !important;
}