How to fix error access to xmlhttprequest at site.ru from origin www.site.ru?

Question

AJAX

Hello, dear programmers...
My site is available both via www and without it... And I noticed such a thing. Suppose a gif is published on the site (shows only a screenshot and a play button, and then when you click on the button, the gif itself is loaded via ajax) at site.ru/gifka.gif. So, if I sit on site.ru and play this gif, it will load and work, but if I go to the site already under www.site.ru and try to play the gif, nothing will work, but in developer console, I get the error "access to xmlhttprequest at site.ru from origin www.site.ru"
How can I fix this?