I don’t use Themes in Firefox, but it sounds like it could be related to:
I have seen around 50 exact clones of my extension, all posted from new accounts with some varied (AI-generated?) names and descriptions. The uploader-account always got a spam-link in their profile (SEO optimization I guess).
I’m not the only one who have had the problem, it seemed AMO was flooded with various clone-extensions. I guess it is very likely there have been or is a similar problem with themes.
If it looks like similar problem, I suggest you tag Edward Sullivan (see the linked thread).