Help with blurry graphics

Any one knows why sometimes graphics get blurry ?! When i open game sometimes graphics became blurry i checked google and its a bugg in wow but they say to go to advanced tab and reduce the rendering such option in the game doesn't exist any suggestions ? Tyvm.

Could you provide a screenshot to see what kind of blur it is?

Problem was fixed i noticed that it has to do with the weather and especially fog in human lands or if u have firefox open and then u run the game!