Not working at all on Etsy. I'm using Firefox 66.02 (64 bit) and just added the Pinterest button today - version 4.0.77. This is very frustrating since Etsy has removed the social media links (a seller can post their own from internal link) for the public to pin products.
I'm able to save from Etsy's front page, individual seller pages, and product pages. May I please have an URL or two to try out? Also, are you using the browser button or a context menu or hovering Save button?