The steps you need to take in order to download the gif file might be different depending on the browser you use.
When prompted you will need to allow Flash to run on Bannersnack.com, we recommend choosing the "Use every time" option so you don't have to select that option every time you want to download.
There are two steps in order to download the gif in chrome. After you clicked on Generate you will have to Allow the flash player in the top left corner of the toolbar as seen in the below screenshot (this needs to be done only once) and also to run the flash plugin in the top right toolbar (you need to do this every time you generate the banner.
You need to click on Generate then in the top toolbar allow the flash player to run on Bannersnack. You only need to do this the first time you generate the gif download.