Really? Have you ever tried to use good 'ol run-of-the-mill Firefox to browse files, photos and videos? Or open local HTML or JS files? Etc...? There's HTML

Really? Have you ever tried to use good 'ol run-of-the-mill Firefox to browse files, photos and videos? Or open local HTML or JS files? Etc...? There's HTML5/Javascript IDEs which run entirely client-side which you can install in the browser's cache, or keep the file in your file system. You can give web apps native features and define how it installs/behaves using the App Manifest. A browser nowadays can do nearly as much as a full OS, even within a full OS.