It's not Firefox, it's the server. Edit and resend the request with header "Accept: image/jpeg" only and you'll most likely get a JPEG file.

That seems more likely. I still hate webp.

what 2 hours ago | parent | prev [-]

Does it actually request the image that it already downloaded again to save it to a file? Seems rather silly?

	▲	ender341341 20 minutes ago \| parent [-]
		No, the server is just sending the file named 'foo.jpg', but encoded as a webp with webp mime type, so when you save the file it defaults to the webp extension cause it ends up treating the filename as a blob of text without an expected extension for the file type.