Would be 5/5 if opened fullscreen

Não funciona. Não cria WebApps como o Edge ou o Chrome fazem.

Worked fine on last year. But not now.

Fantastic addon. I hope this stays maintained.
With a bit of my own work, I used it to create desktop-embedded webpages. With the required "popup window" addon I can just right click a page and send it off to it's own little container on the desktop with no taskbar or switcher entry.

Figured out how to get it to work, thank you for this! It's a concept that I desperately wanted in Firefox, but couldn't figure out how to implement it. The only thing that's a bother, as others pointed out, is the necessity to maximize the window manually, but I read your response to a review on the popup add on saying that this is an issue with Firefox itself.

Horrível. Não funciona

Loved the idea and execution, but https://web.whatsapp.com does not play well in "App Mode" (likely due to Whatsapp's own scripts that assumes there's always a title, menu and/or address bar, throwing mouse pointer navigation off vertically).