Yup that's the one! Apologies as I was away from my computer for a while and couldn't check earlier.

I have a firefox extension that I use at least multiple times a day, that lets me select which format to download an image in - from JPGs (with multiple compression options) to PNG and WEBPs.

I’ll update this post with the name when I have access to my computer.

Edit: The extension is called "Save Webp As"! Thanks @LinkOpensChest_wav@lemmy.one