Firefox

userChrome.css

/* Make tabs look like tabs */
.tab-background {
	border-radius: 0px 0px !important;
	margin-bottom: 0px !important;
 }

 .tabbrowser-tab:not([selected=true]):not([multiselected=true]) .tab-background {
	background-color: color-mix(in srgb, currentColor 2%, transparent);
 }

 menupopup>menu, menupopup>menuitem {
	padding-block: 2px !important;
 }

 :root {
	--arrowpanel-menuitem-padding: 2px !important;
 }

/* Disable fade out on inactive window */
:root[tabsintitlebar] #titlebar:-moz-window-inactive {
	opacity: 1 !important;
}

/* Disable blue dot on pinned tab */
.tabbrowser-tab > .tab-stack > .tab-content[pinned][titlechanged]:not([selected="true"]){
	background-image: none !important;
}