remove reset style for button outlines in firefox

lms/static/sass/base/_reset.scss

@@ -50,6 +50,7 @@ input[type="checkbox"], input[type="radio"] { box-sizing: border-box; padding: 0
 input[type="search"] { -webkit-appearance: textfield; -moz-box-sizing: content-box; -webkit-box-sizing: content-box; box-sizing: content-box; }
 input[type="search"]::-webkit-search-decoration, input[type="search"]::-webkit-search-cancel-button { -webkit-appearance: none; }
 button::-moz-focus-inner, input::-moz-focus-inner { border: 0; padding: 0; }
+button:-moz-focusring { outline: 1px dotted black; }
 textarea { overflow: auto; vertical-align: top; resize: vertical; }
 input:valid, textarea:valid {  }