Up and down arrows do not work in Firefox Developer Edition for input type=number
Seems to work for me on Firefox 89 (as in, the value gets incremented/decremented)
Is it broken for you if you navigate to data:text/html,<meta charset=utf8><input type=number autofocus> and hit the up arrow?
If not, there might be something blocking that behavior on the page (e.g. a keyup event listener or something similar).
If you do see it in the page I sent you, we’d need to investigate more in depth
Sorry, but what means to navigate to data:text/html,<meta charset=utf8><input type=number autofocus>?
Just to mention, that this up and down arrow work in Firefox, but do not work in Firefox Developer Edition.
here “to navigate” means “open the data URL in your browser”. You can copy paste data:text/html,<meta charset=utf8><input type=number autofocus> in the URL bar of a new tab. It will render the html contained in the URL, then you can test the input type=number that will be displayed.