The following authors have presented themes included in the featured as their own, they have mainly manipulated them by reversing the image…
the next step is editing to add spam
https://addons.mozilla.org/en-US/firefox/user/14496741/
Thanks for reporting, @candelora! If the original designers published their themes under a Creative Commons license, re-mixing the themes is ok.
I am concerned about the spam, though. 
These don’t read as very spammy to me (there’s no outbound links or direct calls to action), but I’m tagging @jorgev for a second opinion.
Hi Caitlin,
if it can help you, these are the themes among those submitted, protected by “all rights reserved”:
https://addons.mozilla.org/en-US/firefox/addon/borealis-firefox/ (my theme!!!)
https://addons.mozilla.org/en-US/firefox/addon/beautiful-bird/
https://addons.mozilla.org/en-US/firefox/addon/night-before-christmas/
https://addons.mozilla.org/en-US/firefox/addon/space-case/
then, if you take a look at the Review Log, yesterday I rejected about twenty themes due this reason, so I deduced that all this work could be justified by the project to edit the themes later to insert commercial spam, but obviously it is a hypothesis …
however, there is not only commercial spam, even this type of massive manipulation of other themes can be considered disturbing spam … subjecting images upside down is a nonsense that does not please anyone, it is not very respectful to all users and towards all the authors
We can take down obvious duplicates because we have a policy about that. Other variations are acceptable. But if you think your copyright or license were violated in some way, the only way we can handle this is via a DMCA takedown notice.
Spam we also take down, of course, but only if it’s clearly spam, not only suspected.
Ok. Obviously unable to make the intent process, these themes can not be canceled due to commercial spam.
But my hope was that the concept of spam could be extended to other types of spam, such as systematic-obsessive disorder by low-quality material (about 30 themes copied and manipulated, submitted in a quarter of an hour).
However one of the “overturned” themes is mine and protected by copyright “All Rights Reserved”, so I formally request its cancellation
this is my theme
and this is the theme to be deleted
https://addons.mozilla.org/en-US/firefox/addon/himanshi-khurana/ !!!
Thanks, @candelora. Can you submit a DMCA Notice to Mozilla’s legal team about that theme (and any other themes that infringe your work)? Here are the instructions: https://www.mozilla.org/en-US/about/legal/report-infringement/
We are generally ok with themes of varying quality on AMO, with a few exceptions like excessive blurry, stretched, or pixelated images. People usually also have an easier time finding high quality themes because those are more discoverable through the featured themes collection and top rated themes search.
We’ll still keep our eyes open for spam and other abuse of systems. 