diff -r 000000000000 -r 6474c204b198 toolkit/themes/linux/global/commonDialog.css
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/themes/linux/global/commonDialog.css	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#filler {
+  -moz-margin-start: -8px;
+  -moz-margin-end: -10px;
+}
+
+#iconContainer {
+  -moz-box-pack: center;
+  min-height: 55px; /* maximum icon height + icon margin */
+  min-width: 58px; /* maximum icon width + icon margin */
+}
+
+#info\.icon {
+  max-width: 48px;
+  max-height: 48px;
+  /* The 'spaced' class does this already. It's repeated here to make it clearer
+     what margin values the #iconContainer's min-height and max-height depend on: */
+  margin: 3px 5px 4px;
+}