diff --git a/src/components/views/rooms/RoomList.js b/src/components/views/rooms/RoomList.js
index ad67d8e308..0fe0ff3d8c 100644
--- a/src/components/views/rooms/RoomList.js
+++ b/src/components/views/rooms/RoomList.js
@@ -778,6 +778,9 @@ export default createReactClass({
                     className="mx_RoomList"
                     role="tree"
                     aria-label={_t("Rooms")}
+                    // Firefox sometimes makes this element focusable due to
+                    // overflow:scroll;, so force it out of tab order.
+                    tabindex="-1"
                     onMouseMove={this.onMouseMove}
                     onMouseLeave={this.onMouseLeave}
                 >