Google announced the WebP image format about 8 years ago. This format is much smaller than other traditional image formats, but preserves the good quality of images and helps to download them quickly. It is used in Google Chrome for many years, but not all browsers were able to use it too.
Google tried to convince Mozilla to use WebP as well, but Mozilla rejected this offer and insisted on working with more widely used formats. Now, Mozilla representatives change their opinion and they are ready to integrate WebP support into the Firefox.
The WebP format will be used in all Firefox versions built on the Gecko engine, the version for the PCs, and the Android devices. However, the iOS version will still not support this format.
The transfer will not be fast, it may take many months. It may cause some bug and security issues, so to make the stable version of the Firefox that will work with WebP, developers need to spend hours or coding and fixing errors. They are going to obtain this technology in the first half of 2019.
For most of the users, the changes may be not clearly seen. After the WebP support will be implemented, they may notice the fast loading images and the better performance of Firefox when loading pages with a big number of pictures.