userChrome.css

.tabbrowser-tab:not(:hover) .tab-close-button {
  display: none;
}
.tabbrowser-tab:not([pinned]):hover .tab-close-button {
  display: block !important;
}

.tabbrowser-tab:not([pinned]):hover .tab-icon-image {
  display: none !important;
}

.tabbrowser-tab:hover .tab-throbber,
.tabbrowser-tab:hover .tab-icon-image,
.tabbrowser-tab:hover .tab-sharing-icon-overlay,
.tabbrowser-tab:hover .tab-icon-overlay,
.tabbrowser-tab:hover .tab-label-container,
.tabbrowser-tab:hover .tab-icon-sound {
  -moz-box-ordinal-group: 2 !important;
}

.tabbrowser-tab .tab-close-button {
  margin-left: -2px !important;
  margin-right: 2px !important;
}

/* This removes the tab separators */
.tabbrowser-tab::before,
.tabbrowser-tab::after {
  display: none !important;
}

.tab-background[selected='true'] {
  color: #eceff4 !important;
}

.tabbrowser-tab {
  transition: color 0.25s !important;
  text-align: center !important;
  /*display: inherit;*/
  justify-content: center;
  align-items: center;
}

.tabbrowser-tab[selected='true'],
.tab-label-container[selected='true'] {
  color: #88c0d0 !important;
  /* background-color: var(--color3) !important; */
  /* background-image: linear-gradient(var(--color3), var(--color3)) !important; */
}

/* hide navbar */
#nav-bar:not([customizing]) {
  visibility: visible;
  margin-top: -42px;
  transition-delay: 1s;
  filter: alpha(opacity=0);
  opacity: 0;
  transition: visibility, ease 0.5s, margin-top, ease 0.5s, opacity, ease 0.5s !important;
}

/*
keep visible when urlbar is focused
navbar is hovered
or menubar/customization is open
*/

:root:not([customizing]) :hover > #nav-bar,
#nav-bar:focus-within,
#urlbar[focused='true'],
#identity-box[open='true'],
#navigator-toolbox:hover > #nav-bar:not([customizing]),
#toolbar-menubar:not([inactive='true']) ~ #nav-bar:not([customizing]) {
  visibility: visible;
  margin-top: 0;
  filter: alpha(opacity=100);
  opacity: 100;
}

#nav-bar .toolbarbutton-1[open='true'] {
  visibility: visible;
  margin-top: 0px;
  opacity: 100;
}

/* hide scrollbar  */

:-moz-any(#content, #appcontent) browser {
  margin-right: -17px !important;
  overflow-y: scroll;
  margin-bottom: 0px !important;
  overflow-x: scroll;
}

#TabsToolbar:hover {
  background: transparent;
}

#TabsToolbar. {
  padding-bottom: 30px;
}

.tab-line {
  display: none;
}

tab:not(:active) .tab-background {
  transition: background-color var(--animation-speed) !important;
}
/* deixar a aba ativa em destaque e o resto desfocado */
:root:not([customizing]) :hover > .tabbrowser-tab:not(:hover) {
  filter: blur(0.6px) brightness(88%);
  transition: blur, ease 0.3s !important;
}

:root:not([customizing]) :not(:hover) > .tabbrowser-tab {
  filter: blur(0px) brightness(100%) !important;
  transition: blur, ease 0.2s !important;
}

/* sumir com o nome da aba depois de um tempo */

/* #tabbrowser-tabs .tab-label-container[customizing] {
  color: transparent;
  transition: ease 0.5s;
  transition-delay: 3s;
} */

:root:not([customizing]) :hover > #tabbrowser-tabs,
:root:not([customizing]) #tabbrowser-tabs:focus-within,
#urlbar[focused='true'],
#identity-box[open='true'],
#navigator-toolbox:hover > #tabbrowser-tabs:not([customizing]),
#toolbar-menubar:not([inactive='true']) ~ #tabbrowser-tabs:not([customizing]) {
  color: #d8dee9 !important;
  /* opacity: 0.25;
  transition: linear 0s;
  transition-delay: 3s; */
}

:root[uidensity='compact'] {
  --tab-min-height: 32px !important;
}

tab:not([selected]):hover .tab-background {
  background-color: #3b4252 !important;
  transition: background-color ease 100ms !important
}

.tab-close-button {
  list-style-image: url('active_close.png');
  transition: list-style-image var(--animation-speed) ease-out !important;
}
.tab-close-button:hover {
  list-style-image: url('mouseover_close.png');
}

/* Removal of black bottom 1px line */
#navigator-toolbox::after {
  display: none !important;
}

#urlbar {
  border-radius: 5px !important;
  height: 36px;
}

.urlbar-input-box {
  padding: 5px 5px !important;
  background: rgba(59, 66, 82, 0.6);
  border-radius: 1.5px !important;
}

.urlbar-input-box>.urlbar-input {
  color: #eceff4;
}

/*
 * Originally from:
 * http://forums.mozillazine.org/viewtopic.php?p=14404121#p14404121
 */

#urlbar {
  position: relative;
  z-index: 1;
  border-radius: 6.8px !important;
}

#urlbar #urlbar-input {
text-align: center !important;
}

#identity-box:after {
  content: '';
  position: absolute;
  height: 100%;
  width: 100%;
  top: 0;
  left: 0;
  pointer-events: none;
  z-index: -1;
  background-color: #2e3440;
  opacity: 0.5;
}

/* There is also grantedPermissions, but irrelevant. */

/* about:about */
#urlbar[pageproxystate='valid'] #identity-box.unknownIdentity:after {
  background: #bf616a; /* Firefox Red 50 */
}

/* about:config */
#urlbar[pageproxystate='valid'] #identity-box.chromeUI:after {
  background: #5e81ac; /* Firefox Blue 50 */
}

/* uBlock Origin Dashboard */
#urlbar[pageproxystate='valid'] #identity-box.extensionPage:after {
  background: #81a1c1; /* Firefox Blue 40 */
}

/* https://www.github.com/ */
#urlbar[pageproxystate='valid'] #identity-box.verifiedIdentity:after{
  background: #a3be8c; /* Firefox Green 70 */
}

/* https://www.google.com/ */
#urlbar[pageproxystate='valid'] #identity-box.verifiedDomain:after{
  background: #a3be8c; /* Firefox Green 60 */
}

/* https://mixed-script.badssl.com/ */
#urlbar[pageproxystate='valid'] #identity-box.mixedActiveBlocked:after {
  background: #a3be8c; /* Firefox Green 50 */
}

/* https://mixed.badssl.com/ */
#urlbar[pageproxystate='valid'] #identity-box.mixedDisplayContent:after {
  background: #d08770; /* Firefox Yellow 60 */
}

/* https://very.badssl.com/ */
#urlbar[pageproxystate='valid'] #identity-box.mixedDisplayContentLoadedActiveBlocked:after {
  background: #d08770; /* Firefox Yellow 60 */
}

/* https://self-signed.badssl.com/ but add certificate exception */
#urlbar[pageproxystate='valid'] #identity-box.certUserOverridden:after {
  background: #ebcb8b; /* Firefox Yellow 50 */
}

/* Don't know an example for this */
#urlbar[pageproxystate='valid'] #identity-box.weakCipher:after {
  background: #ebcb8b; /* Firefox Yellow 70 */
}

/* https://mixed-script.badssl.com/ but disable protection */
#urlbar[pageproxystate='valid'] #identity-box.mixedActiveContent:after {
  background: #bf616a;  /* Firefox Red 60 */
}

/* http://http-login.badssl.com/ */
#urlbar[pageproxystate='valid'] #identity-box.insecureLoginForms:after {
  background: #bf616a;  /* Firefox Red 70 */