https://techcrunch.com/2018/06/05/firefox-launches-side-by-side-browsing-and-a-theme-editor-as-test-pilot-experiments/

Mozilla’s Firefox is back in the browser game, thanks to its recent updates which now allow it to once again challenge the likes of Google’s Chrome browser. One thing that always made Firefox stand out was its willingness to experiment. In recent years, the organization channeled many of these experiments through its Test Pilot program and today, it’s launching two new projects through this project: Firefox Color and Side View.

Firefox Color does pretty much what you probably expect it to do. It’s essentially a theme editor that allows you to pick the colors in your browser and even set textures for things like your background, for example.