Zotero Connector in Firefox saves multiple copies of same reference
I don't know if I am the only person who cannot handle the connector properly: Am using Firefox 76.0.1 with Zotero 5.0.87. I have more than 10 group libraries, plus my personal library. When I click on the "Save to Zotero" button in FF, it drops down the "Saving to" button in which the last library selected in Zotero is shown. By the time I pull down that menu, select "More..." and choose another library/folder, it has already saved to the original library and now it saves in the new library as well, or saves multiple copies in the same library. Or if I click done too quickly, it saves nothing. I am simply not able to predict. Multiple copies is the norm.
The Connector saves immediately to the collection selected in Zotero. If you choose another location from the save popup, the item is moved there and removed from the original location. In the case of a different library, the original item is deleted. Within the same library, it's just the same item — which will always exist in the library root — that's moved between collections.
"Done" has no effect other than closing the popup.
I went to a newspaper article (https://tinyurl.com/ybn8bdcz). Zotero pointer was at that time in a group library. When I clicked on the Connector, I clicked on the drop down menu and chose "My library" and left things there (no 'done' button showed up anyway). After a few seconds, the connector window disappeared. When I went to My library, it showed 2 items had been added to library (see screenshot at https://tinyurl.com/y9l4o4t5
Basically, when you save an item from a page, it creates a "save session" in Zotero with information on the items saved, and if any time after that while on the same page you select a different library, it recreates all items registered in that save session to the new library and deletes the originals. Here, it looks like there were two copies of the item in your personal library that were already registered in the save session. So something caused there to be two items saved, but that problem happened previously in your personal library, so what this debug output shows isn't relevant.
One possibility might be that you double-clicked the save button instead of single-clicking it, causing two items to be saved initially. I can't get that to happen, though.