override gemini-scrollbar CSS to stop the scrollview from pushing out the container, causing FF's flexbox to adapt and keep growing infinitely

src/skins/vector/css/common.css

@@ -47,6 +47,14 @@ a:visited {
     color: #76cfa6;
 }
 
+/* XXX: critical hack to GeminiScrollbar to allow them to work in FF 42 and Chrome 48.
+   Stop the scrollbar view from pushing out the container's overall sizing, which causes
+   flexbox to adapt to the new size and cause the view to keep growing.
+ */
+.gm-scrollbar-container .gm-scroll-view {
+  position: absolute;
+}
+
 .mx_ContextualMenu_background {
     position: fixed;
     top: 0;