Pretty sure this is by design. Firefox image pasting looks pretty difficult to deal with, so this is the team’s best effort. See the relevant comment in the code here:
Right-click “copy image” followed by Ctrl+V pasting works fine for me on Firefox. (44.0.2 on Ubuntu Gnome 15.10).
However, as of this afternoon, I no longer seem to be able to use drag-and-drop image upload in Firefox, either here or on SitePoint. Firefox updated this morning, so that’s probably when the change occurred.
it did not work because the image you posted was not uploaded to meta.discourse.org https://pixabay.com/static/uploads/photo/2016/01/30/17/41/africa-1170108_960_720.jpg
This is the image link.
But this seems to be doing what the elephant picture did (above) and linking to pixabay, rather than uploading to Discourse. (And the original report was using images on imgur, so it seems not to be the image or the site.)
If there is an image in the clipboard, copied from any other application, pasting in Firefox works fine.
If the image was copied in Firefox using Copy Image, pasting no longer gives our application the data that we can parse, and only gives us the URL.
I think Discourse is doing the right thing in this case. Since it doesn’t have the image data to upload, it inserts the URL in the document as if that was copied and pasted.
However when I right click on the image in the Discourse page and Copy, then Paste into the onebox, I instead get a PNG which then gets converted by Discourse into the following JPG;
any thoughts? I am guessing this is not the intended behavior either?