In addition to the point about "not being expected to do a full malware analysis"...

Assuming the malware doesn't clean up after itself, `pacman -Q firefox-patch-bin librewolf-fix-bin zen-browser-patched-bin` would tell you if they are installed... but if it did clean up after itself... how are the maintainers supposed to know what steps were taken to clean up given that it's a rat that could be running different steps on different computers...