This download dialog is due to an issue on Google’s end and is happening throughout the ecosystem.
To provide a bit of context here—the file has to do with MIME type. Typically these files will automatically download for you, however in some special circumstances (like referencing the file via a script tag) it loads the file directly rather than downloading it."
Although understandably frustrating for some users to encounter, We can assure you that this is not something that should cause concern, and Google and their ad protection partners are looking into ways in which this is preventable from happening to their clients and users.
Once I have some more information on this issue I will get back to you with further updates.
Thanks again for bringing this to our attention,