Bug 1511652 - Override the :-moz-focusring outline on Ctrl+Tab previews on Windows. r=bgrins

Differential Revision: https://phabricator.services.mozilla.com/D13622

--HG--
extra : moz-landing-system : lando

browser/themes/shared/ctrlTab.inc.css

@@ -24,6 +24,8 @@
   -moz-appearance: none;
   /* !important overrides the :hover color from button.css on Linux */
   color: inherit !important;
+  /* remove the :-moz-focusring outline from button.css on Windows */
+  outline: none !important;
   margin: 0;
   text-shadow: 0 0 1px hsl(0,0%,12%), 0 0 2px hsl(0,0%,12%);
 }