My Firefox UserChrome.css

UserChrome.css

/* Line on Tabs */
#TabsToolbar .tabbrowser-tab[selected] .tab-line {
  display: none !important;
}

/* Back Button */
#back-button:not(:hover),
#back-button:not(:hover) > .toolbarbutton-icon {
  background: transparent !important;
  border: none !important;
  border-color: transparent !important;
  box-shadow: none !important;
}

#back-button:hover,
#back-button:hover > .toolbarbutton-icon {
  background: transparent !important;
  border: none !important;
  border-color: transparent !important;
  box-shadow: none !important;
}

:root:not([uidensity="compact"])
  #nav-bar-customization-target
  #back-button
  > .toolbarbutton-icon {
  border-radius: 4px !important;
  width: auto !important;
  height: auto !important;
  padding: 6px !important;
}

:root:not([uidensity="compact"])
  #nav-bar-customization-target
  #back-button:not([disabled]):not([open]):hover
  > .toolbarbutton-icon {
  background-color: var(--toolbarbutton-hover-background) !important;
}

:root:not([uidensity="compact"]) #back-button {
  margin-left: 6px !important;
  margin-top: 3px !important;
  margin-bottom: 3px !important;
}

/* Send to Device Context Menu */
#context-sendpagetodevice,
#context-sep-sendpagetodevice,
#context-sendlinktodevice,
#context-sep-sendlinktodevice,
#context_sendTabToDevice,
#context_sendTabToDevice_separator {
  display: none !important;
}

/* Dot Blue Hide */
.tabbrowser-tab:-moz-any([image], [pinned])
  > .tab-stack
  > .tab-content[attention]:not([selected="“true”"]),
.tabbrowser-tab
  > .tab-stack
  > .tab-content[pinned][titlechanged]:not([selected="“true”"]) {
  background-image: none !important;
}

/* Back Button */
.panel-header > .subviewbutton-back {
  border-radius: 6px !important;
}

/* Hide Tab Line Color */
#tabbrowser-tabs {
  --tab-line-color: none !important;
}

/*  Hide Open Link in Container */
#context-openlinkinusercontext-menu {
  display: none !important;
}