use standard CSS for a focused CodeMirror outline

edit/codemirror-default.css

@@ -15,8 +15,7 @@
   -webkit-animation: highlight 3s cubic-bezier(.18, .02, 0, .94);
 }
 .CodeMirror-focused {
-  outline: -webkit-focus-ring-color auto 5px;
-  outline-offset: -2px;
+  outline: #7dadd9 auto 1px; /* not using the ring-color hack as it became ugly in new Chrome */
 }
 .CodeMirror-bookmark {
   background: linear-gradient(to right, currentColor, transparent);
@@ -24,13 +23,6 @@
   width: 2em;
   opacity: .5;
 }
-@supports (-moz-appearance:none) {
-  /* restrict to FF */
-  .CodeMirror-focused {
-    outline: #7dadd9 auto 1px;
-    outline-offset: -1px;
-  }
-}
 .CodeMirror-search-field {
   width: 10em;
 }