Hi there, @antoyo. First off, thanks for your wonderful and powerful add-on. It has relieved many headaches of rearranging and renaming bookmarks. This is definitely an accessibility feature, I hope it can be restored for us Pale Moon users.
In fact, it's been pretty useful at what it does, I had to modify the xpi (adding our own GUID and a lower minimal install/version number) so I could install the latest and compatible version available. Although, that isn't the case anymore since v27.1 of Pale Moon. PMkit, is an alternative library that provides a basic compatibility layer with the Mozilla's Add-on SDK. Many add-ons have already been successfully adapted and work fine in Pale Moon. Thus, it's progressing greatly as another option for our add-on developers.
Additionally, if you could fully and officially support us please, that would be awesome. You can do this by adding our GUID/application block to the install.rdf, fixing any bugs that pertain to us, and hosting it on APMO or AMO. But, that is only one of the options to support us. We offer several other alternatives.
Not to mention, Pale Moon uses it's own layout and rendering engine called Goanna. This was put in place because "Pale Moon is not Firefox, and never will be again." Hence, the UI differences and the in-progress/future Road Map.
-PS: I'm not an add-on developer or in charge of this process, just a Pale Moon enthusiast. You would need to get in contact with Andrew Gilbertson (AndyTheAbsurd) or Lootyhoof (Ryan659), at our forums.