Fps drops in android browser

Fps drops in some android devices browser such as Samsung S2. Its works Properly when run as apk but on android broswser FPS drops from 60 to 30 just by adding one sprite on screen with no update loop or timer.
I am new to cocos2d-js. Can anyone please guide me about it?
I am adding sprite as below

        var size = cc.winSize;
        var BG = new cc.Sprite(res.popupBgPng);
        this.scaleFactor = (size.height) / BG.height;
        BG.x = size.width / 2;
        BG.y = size.height / 2;
        BG.scale = this.scaleFactor;
        this.addChild(BG);

Please guide.