Firefox: userchrome.css

/* Use color and shape to make the tabs look more like tabs */
.tab-background {
background: #0000FF;
border-radius: 18px 18px 18px 18px !important;
margin-bottom: 3px !important;
box-shadow: 0 0 2px 2px rgba(0,0,0,0.1) !important;
border: 1px solid rgba(0,0,0,.5) !important;
}
/*Selected*/
.tabbrowser-tab[selected] .tab-background {
background: #FCB731 !important;
}

/* Hover over tabs */
.tabbrowser-tab:hover .tab-background:not([selected]) {
background: #FF0000 !important;
}

/*Not Selected*/
.tabbrowser-tab:not([selected]) .tab-label {
color: white !important;
}

/* Make tab labels scroll continuously */
.tab-label-container {
overflow: hidden !important;
display: block !important;
}

.tab-label {
animation: tabTextScroll 8s linear infinite !important;
white-space: pre !important; /* Forces the text to stay on one line */
padding-left: 100% !important; /* Starts the text completely off-screen */
line-height: 32px !important; /* Adjust this number if your tab height is custom */
vertical-align: middle !important; /* Aligns the inline element to the middle */
}

@keyframes tabTextScroll {
0% { transform: translate(0, 0); }
100% { transform: translate(-100%, 0); }
}