userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
/*https://pastebin.com/bRNs2S9B*/

/* ---------------------------- TABS ---------------------------- */

/* hide decorative line above tabs */
.tab-line {
    display: none;
}

/* hide left tab bar gap */
.titlebar-placeholder[type="pre-tabs"] {
    width: 0 !important;
    opacity: 0 !important;
}

/* hide right tab bar gap. 3px prevents visual bug */
.titlebar-placeholder[type="post-tabs"] {
    width: 3px !important;
}

/* experimenting with ways to hide window controls, doesn't work */
.titlebar-placeholder[type="caption-buttons"], #window-controls {
/*  background: #3C3C3C !important; */
/*  display: none !important; */
}

/* inactive tab text, background */
.tabbrowser-tab:not([selected="true"]) {
    color: #CCCACA !important;
}

/* inactive tab hover */
.tabbrowser-tab:not([selected="true"]):hover {
}

/* active tab text, background */
.tabbrowser-tab[selected="true"] {
    color: #CCCACA !important;
    border-bottom: none !important;
}


/* hide favicons */
.tabbrowser-tab .tab-icon-image {
    display: none !important;
}

/* show favicons on pinned tabs though */
.tabbrowser-tab[pinned]:not([busy="true"]) .tab-icon-image {
    display: block !important;
}

.tabbrowser-tab[pinned] {
    display: -moz-box !important;
}

/* hide vertical tab separators */
.tabbrowser-tab::after, .tabbrowser-tab::before {
    border: none !important;
}

/* disable tab text overflow fading */
.tab-label-container[textoverflow]:not([pinned]) {
    mask-image: unset !important;
}

/* up to full width tabs */
.tabbrowser-tab:not([pinned]) {
    min-width: 0px !important;
/*  max-width: 100% !important;  */
}

/* ------------------------- ADDRESS BAR ------------------------- */

/* hide various buttons */
#back-button,
#forward-button,
.tab-close-button,
#pageAction-urlbar-jid1-xufzosoflzsoxg_jetpack,
#pageActionSeparator,
#pageActionButton,
#alltabs-button,
.urlbar-history-dropmarker {
    display: none;
}

/* hide border highlight on active urlbar, colour urlbar like container */
#urlbar {
    border-color: transparent !important;
    background-color: inherit !important;
}

/* hide line between navbar and tabs */
#nav-bar {
    box-shadow: none !important;
}

/* hide line below navbar */
:root {
    --toolbox-border-bottom-color: none !important;
}

#reader-mode-button[readeractive="true"] {
    filter: grayscale(100%) brightness(30) !important;
}

#identity-icon,
#identity-icon-labels {
    display: none !important;
}

#identity-box {
    padding: 0px !important;
    border-right: 0px solid !important;
}

/* ---------------------------- MISC ---------------------------- */

/* hide context menu items */
#context-viewpartialsource-selection {
    display: none;
}

/* consistency for my VS borders */
#main-window[sizemode="normal"] {
/*  margin-top: 7px !important; */
    margin-top: 2px !important;
}

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


#TabsToolbar {
/*  visibility: collapse !important; */
}

#titlebar {
/*  display: none !important; */
}

#navigator-toolbox {
/*  display: none !important; */
}