In Windows the issue is that alt+space will by default open the window's control menu (for minimize/maximize/move/etc.). Pressing space down and then alt will work though.
Probably because firefox has alt+(left|right)arrow as global navigation bindings, and is capturing them before the captcha can get them. requesting a fullscreen gaming mode avoids more key binding issues, but probably ruins the "captcha" feel.
nice, that was the first thing that I noticed that I kept trying to do. It makes it a lot easier. I forgot about how clunky controls can be for older games without retroarch rebinds and stuff. I was playing Perfect Dark last night on my Steamdeck and I was able to bind the controls to a modern layout (left-stick walk, right-stick look, etc...) and it makes the game a ton easier.