You have configured a data control rule to block images and archive transfers if the destination is Firefox. Now you are trying to install Firefox plugins, but it isn't working.
First seen in
Enterprise Console 4
Endpoint Security and Control 9
What To Do
You can temporarily allow image and archive transfers in Firefox before installing plugins. When you've installed the plug-in, switch the protection back on.
Firefox plugins are stored in .xpi format, which is a type of archive file, so the data control scanner correctly blocks their transfer.