Fix flexbox for Firefox OS

src/stylesheets/Lungo.layout.nav.styl

@@ -14,6 +14,7 @@ nav
   &.groupbar, footer &
     display-box()
     box-pack(justify)
+    width: 100%
     & > a
       box-flex(1)
 
@@ -64,7 +65,7 @@ nav
 
 
   &.groupbar
-    position: absolute
+    position: relative
     top: HEADER_FOOTER_HEIGHT
     height: HEADER_GROUPBAR_HEIGHT
     width: 100%

src/stylesheets/Lungo.layout.styl

@@ -75,7 +75,7 @@ header, footer
   left: 0
   width: 100%
   display: block
-  z-index: 2
+  z-index: 1
 
 header
   top: 0