Adverisement. Announcement

Hello, have problem this time with weird "ad" Im using mozilla firefox and its looks fine:
https://2img.net/h/i1090.photobucket.com/albums/i376/CieniuPL/Error2_zpsfbd74e89.png

But 2nd admin is using chrome and 1-3 times for an hour the ad is moving and looks like this:
https://2img.net/r/ihimizer/img577/1585/amini.png

You see ? This announcement is very important for our forum because its giving bonus to a members, how can it be fixed?

This ad, go upper and replacing the important text, cannot close it or something, moving is wrong word, its just appear at the header and cant see this important text from 1st screenshot.

http://pokehelvetti.forumpl.net/

But is in construction, like i told This ad is appearing in header sometimes in Chrome, on firefox is everything fine.

Do you mean that the ad is blocking/covering part of the announcement?

Do you mean that the ad is blocking/covering part of the announcement?

Yes but im using Mozilla Firefox as primary browser, have here adblock so everything is fine. Used yday Opera for 2hours and maybe 4-5 times this happened.

Any way to fix it or it just happen?