Merge pull request #4193 from MarcoZehe/FixExtraneousTabStopOnTree

Remove extraneous tab stop from room tree view.

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}
                 >