--- a/browser/themes/shared/tabs.inc.css
+++ b/browser/themes/shared/tabs.inc.css
@@ -699,27 +699,27 @@
 /* Also show separators beside the selected tab when dragging it. */
 #tabbrowser-tabs[movingtab] > .tabbrowser-tab[visuallyselected]::before {
   content: "";
   display: -moz-box;
 }
 
 /* Tab bar scroll arrows */
 
-.tabbrowser-arrowscrollbox > .scrollbutton-up,
-.tabbrowser-arrowscrollbox > .scrollbutton-down {
+#tabbrowser-tabs > .tabbrowser-arrowscrollbox > .scrollbutton-up,
+#tabbrowser-tabs > .tabbrowser-arrowscrollbox > .scrollbutton-down {
   list-style-image: url(chrome://browser/skin/arrow-left.svg);
   -moz-context-properties: fill, fill-opacity;
   fill: currentColor;
   fill-opacity: var(--toolbarbutton-icon-fill-opacity);
   color: inherit;
 }
 
-.tabbrowser-arrowscrollbox > .scrollbutton-up:-moz-locale-dir(rtl),
-.tabbrowser-arrowscrollbox > .scrollbutton-down:-moz-locale-dir(ltr) {
+#tabbrowser-tabs > .tabbrowser-arrowscrollbox > .scrollbutton-up:-moz-locale-dir(rtl),
+#tabbrowser-tabs > .tabbrowser-arrowscrollbox > .scrollbutton-down:-moz-locale-dir(ltr) {
   transform: scaleX(-1);
 }
 
 /* New tab button */
 
 .tabs-newtab-button,
 #TabsToolbar > #new-tab-button ,
 #TabsToolbar > toolbarpaletteitem > #new-tab-button {

--- a/toolkit/themes/osx/global/tabbox.css
+++ b/toolkit/themes/osx/global/tabbox.css
@@ -35,24 +35,16 @@ tab {
   padding-top: 1px;
 }
 
 tab:-moz-focusring {
   /* Tab focus rings need to overlay adjacent tabs. */
   position: relative;
 }
 
-tab:first-of-type {
-  padding-inline-start: 2px;
-}
-
-tab:last-of-type {
-  padding-inline-end: 2px;
-}
-
 tab[visuallyselected="true"]:not(:-moz-window-inactive) {
   color: #FFF;
 }
 
 @media (-moz-mac-yosemite-theme: 0) {
   tab[visuallyselected="true"] {
     color: #FFF;
     text-shadow: rgba(0, 0, 0, 0.4) 0 1px;