Every web developer would come across this issue. In Firefox, when you’d clicked a image or link there you’ll see a dotted border around the image or link. It makes ugly to the website. I googled around this issue & found a way to resolve it. If you see the image below you could easily identify the bug.

To resolve this issue just a single line css is enough.

<style type="text/css">
a:active, a:focus{outline: 0;}
</style>;

Courtesy:  mycodings.blogspot.com