Fix thumbnail reordering

Don't use Array.prototype.sort() because (1) it operates in place and,
thus, mutes the Redux state and (2) it is not necessarily stable and,
thus, unnecessarily shuffles the thumbnails.

react/features/filmStrip/components/FilmStrip.js

@@ -33,18 +33,7 @@ class FilmStrip extends Component {
                     showsHorizontalScrollIndicator = { false }
                     showsVerticalScrollIndicator = { false }>
                     {
-                        this.props.participants
-
-                            // Group the remote participants so that the local
-                            // participant does not appear in between remote
-                            // participants.
-                            .sort((a, b) => b.local - a.local)
-
-                            // Have the local participant at the rightmost side.
-                            // Then have the remote participants from right to
-                            // left with the newest added/joined to the leftmost
-                            // side.
-                            .reverse()
+                        this._sort(this.props.participants)
                             .map(p =>
                                 <Thumbnail
                                     key = { p.id }
@@ -54,6 +43,40 @@ class FilmStrip extends Component {
             </Container>
         );
     }
+
+    /**
+     * Sorts a specific array of <tt>Participant</tt>s in display order.
+     *
+     * @param {Participant[]} participants - The array of <tt>Participant</tt>s
+     * to sort in display order.
+     * @private
+     * @returns {Participant[]} A new array containing the elements of the
+     * specified <tt>participants</tt> array sorted in display order.
+     */
+    _sort(participants) {
+        // XXX Array.prototype.sort() is not appropriate because (1) it operates
+        // in place and (2) it is not necessarily stable.
+
+        const sortedParticipants = [];
+
+        // Group the remote participants so that the local participant does not
+        // appear in between remote participants. Have the remote participants
+        // from right to left with the newest added/joined to the leftmost side.
+        for (let i = participants.length - 1; i >= 0; --i) {
+            const p = participants[i];
+
+            p.local || sortedParticipants.push(p);
+        }
+
+        // Have the local participant at the rightmost side.
+        for (let i = participants.length - 1; i >= 0; --i) {
+            const p = participants[i];
+
+            p.local && sortedParticipants.push(p);
+        }
+
+        return sortedParticipants;
+    }
 }
 
 /**