Firefox extension to overlay format and JPEG quality buttons on inline or stand-alone images for quickly saving a converted version of the image.
URL on AMO: https://addons.mozilla.org/firefox/addon/save-webp-as-png-or-jpeg/
Screenshots:
You can remove unwanted Save/Copy/Re-request buttons on the Options page (click the gear button):
When an image is displayed stand-alone, the bar and the info panel appear automatically for WebP images:
(Added in v1.5) New workarounds for restricted pages, including sites that "sandbox" their content:
