No, this allows you to use all png images without having to re-write vBulletin templates to do so.
Your browser will first look for a .gif file, if its not found, it sends a 404 error and thus a broken image. We use a custom 404 file to redirect to the same named image but .png and forward it to your browser.
So for example
https://vborg.vbsupport.ru/images/cs...ser_online.gif 
Normal image, you remove
https://vborg.vbsupport.ru/images/cs...ser_online.gif and add
https://vborg.vbsupport.ru/images/cs...ser_online.png the 404 file will redirect to this instead.