How do I open app with a correctly sized window?

HI folks,

I understand that I can't open a PWA in a full screen without interacting with the browser first. (Although I get conflicting results when I do with FF/Safari/Chrome)

What I do want to do is control how the screen is opened. Right now it appears to open in the window of the browser, leaving a huge white space as the window was bigger than the app display.

Can I resize the browser window automatically to fit the app? Or how can I ensure it looks right when you launch it.

Here's how it presents in FF: snag.gy/pIOUcR.jpg

and if I go full screen I get: snag.gy/DQ0gz2.jpg

Yet, if I use Safari its fine on full screen, using the exact same published PWA: snag.gy/o5iM2S.jpg

Can anyone tell me how I can standardize it so it works across the board?

Thanks