we're having a similar issue here - we cannot download ai-images anymore. We're working as team and are using Firefox 61.0.1 (32-Bit) and IE 11.0.75 and windows 10 (Adobe CC 2018). It doesn't work neither in Firefox nor in IE.
Branching into a new discussionHi Sabine,I apologize for the troubles that you're facing.We've identified this issue and our engineers are working on the fix for the same. Currently you can download the licensed version of the AI files directly.Regards,Sheena