HTML, CSS, Vanilla JS (Mobile first)

I'm not sure how long you've been coding for, but it's smart that you're using min-width media queries. I've been coding for around 9 months and I only just started doing that in the past few months. It's made styling so much easier to do the mobile styling first, then scale up to the desktop.

But Firefox currently does the same thing the screenshot is showing And Chrome seems to look like you wanted it too

Interesting kind of like how I found Chrome does not like... Justify-content left or right but wants flex-start or flex-end it seems that Chrome can Justify content space between with no set height on the element. so you have Margin 0 being inherited on your inputs and have the form set space evenly but seems that Firefox will not do it without a height on the container so it knows how much space it has. So you can either add margin to your inputs or give the container a fixed height and I think things will will work then in both browsers.

maybe someone smarter than me can jump in and help us out with better information