Fix the footer in Firefox

Author: Chasen Le Hara

static/layout.less

@@ -5,7 +5,7 @@
   align-items: stretch;
   flex-wrap: nowrap;
   box-sizing: border-box;
-  height: 100%;
+  height: calc(~"100% - 53px");// 53px header
   -webkit-overflow-scrolling: touch;
   padding-bottom: 0;
   transition: padding-bottom @transition-speed ease;