Upload file directly from a URL in upload (File/Open) dialog On Windows, if I go to a web site that needs a file upload, I can paste a URL into the "Open" dialog box that pops up, and Windows will download the file and upload a temporary version of it to the web site.

Is there an equivalent on the Mac?  If I hit ⌘+⇧+G, and type in a URL, it says 'The folder can't be found'.
The Go To Folder command you mention (command-shift-G) will only navigate your locally mounted volumes, it doesn't understand URLs.  I've never seen anything on the Mac that has the function you specify..