Clicking Download launches Script Editor


WHenever I try to download something through a web browser, Script Editor is launched and tries to open the file. Sometimes I can then go back to the browser and select Save Page As and download the actual file. But when I've got a 90 MB file that's downloaded through a script (as opposed to a link, where I can successfully select "Save Link Target As" ) it's a problem.

It happens in every browser, so clearly I have a setting wrong somewhere.

Any one have any idea where that might be?