Never could see the difference between a so called web app and a shortcut to the site in question on the desktop. It is not a standalone application when it depends on the browser runtime. Much rather prefer Mozilla's sadly vanished application platform, where you could create powerful standalone cross platform desktop applications with knowledge of just XML(XUL being a subset) and Javascript. Firefox and Thunderbird themselves were great examples of such apps and it would have been any day a better alternative to Electron, these applications actually respected the look and feel conventions of each OS they ran on.

Mozilla had a separate XULRunner runtime to bundle with your app for it to be fully standalone, or you could invoke it with the locally installed Firefox instance. There were several, like Songbird (media player), FireFTP/FireSSH (originally began as extensions and now available as standalone software)