Lord only knows why the Category Image field gives us no way of uploading, or inserting a fucking image.
I'm so filled with RAGE at this point, because I've spent two hours on the absolute mess that is the EE filemanager.
2 hours figuring out how to make the filemanager appear and populate a farking text field with the filename.
Anyway.
Download the accessory and rename the download folder to catshit
Insert the catshit folder to your system/third_party folder and activate the accessory.
The function it gives is ONLY available when editing categories on the publish page, simply double click the Image Category field and up will pop the file manager. et voila.