--- a/browser/themes/shared/tabs.inc.css
+++ b/browser/themes/shared/tabs.inc.css
@@ -340,16 +340,17 @@
 }
 
 /* Tab Overflow */
 .tabbrowser-arrowscrollbox > .arrowscrollbox-overflow-start-indicator:not([collapsed]),
 .tabbrowser-arrowscrollbox > .arrowscrollbox-overflow-end-indicator:not([collapsed]) {
   width: 18px;
   background-image: url(chrome://browser/skin/tabbrowser/tab-overflow-indicator.png);
   background-size: 17px 100%;
+  background-repeat: no-repeat;
   border-left: 1px solid;
   border-image: linear-gradient(rgba(255,255,255,.2),
                                 rgba(255,255,255,.2) calc(100% - 1px - var(--tab-toolbar-navbar-overlap)),
                                 transparent calc(100% - 1px - var(--tab-toolbar-navbar-overlap)));
   border-image-slice: 1;
   pointer-events: none;
   position: relative;
   z-index: 3; /* the selected tab's z-index + 1 */