Hi
Tamás,
Thanks for sending us your files. I open it on in GWD and I can correctly see the animation and images when preview in Firefox (see the screenshot below). So I wonder what version of Firefox you have on your machine and what OS you are on? (I am using Firefox v39 on mac) Can you clear the browser cache in Firefox and try preview again?
I also notice that one of image file names in your file has a special character in it
(assets/_0001_Andr†ssy.jpg) and when I open your file in GWD and check the Image PI, the special character is missing from the image file name. Can you correct it and try preview again?
If the problem still happens after you clear the browser cache and correct the image file name, can you try one more thing? Can you turn on the web console when preview the banner file in Firefox? Just right click on the page and select Inspect Element in the context menu and click on Console tab (see the screenshot below). I would like to see if there is any errors when you preview the banner in firefox.
Thanks,