I’m not so sure that they only download. On macOS, Firefox (and Chrome) sometimes stop working in odd ways when they do the background ”download”. For example, file pickers stop functioning or tabs stop loading. All of this starts working again after restarting and letting it update. It’s happens more than a handful of times every year. Enough so that I’ve picked up on the pattern that it only happens when I see it say “update” by the settings menu.