Where can I find help for the Firefox Developer's menu which appears after pressing F12 ? I have tried to download via it a YouTube music and save it as follows but it doesn't replay: What's wrong with this `curl` command ? curl "https://r3---sn-2gb7sn7k.googlevideo.com/videoplayback?expire=1618934363&ei=-6V-YMyVKde0gQeAw42YDg&ip=94.112.85.61&id=o-AP6SpCFdGAWmLzhSgFAtZ3SlEFZ8Ia9CE6Zo6JS4tDTC&itag=397&aitags=133"%"2C134"%"2C135"%"2C136"%"2C160"%"2C242"%"2C243"%"2C244"%"2C247"%"2C278"%"2C394"%"2C395"%"2C396"%"2C397"%"2C398&source=youtube&requiressl=yes&mh=wS&mm=31"%"2C26&mn=sn-2gb7sn7k"%"2Csn-4g5ednsy&ms=au"%"2Conr&mv=m&mvi=3&pl=18&initcwndbps=1492500&vprv=1&svpuc=1&mime=video"%"2Fmp4&ns=oGOAXGyOlcIjz_s85Q2pnIEF&gir=yes&clen=149420529&dur=18529.041&lmt=1562702145590600&mt=1618912361&fvip=3&keepalive=yes&fexp=24001373"%"2C24007246&c=WEB&txp=5532432&n=1YA_uOdo4b3FiA&sparams=expire"%"2Cei"%"2Cip"%"2Cid"%"2Caitags"%"2Csource"%"2Crequiressl"%"2Cvprv"%"2Csvpuc"%"2Cmime"%"2Cns"%"2Cgir"%"2Cclen"%"2Cdur"%"2Clmt&lsparams=mh"%"2Cmm"%"2Cmn"%"2Cms"%"2Cmv"%"2Cmvi"%"2Cpl"%"2Cinitcwndbps&lsig=AG3C_xAwRgIhANfqcvaLCOf7GyvgoJdpRa5Ao5FeICYE2tO48YQbNWudAiEA2fsHoGqkNrm95J4OZTLNnl7-uWKl2oFuDk_mtMxGgNM"%"3D&alr=yes&sig=AOq0QJ8wRAIga4VjSJrXvQQNqTv44Ek_BJrY3xqK-kFSEEIVRd-LuxkCIBSgG30TBv7HqsvzOWJ7JA319KcRe_Ff2RU5VrH7cf-k&cpn=1I6CI7Oh9Q3CxGi2&cver=2.20210418.07.00&range=0-27199999977014&rn=366&rbuf=119795" -H "User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:87.0) Gecko/20100101 Firefox/87.0" -H "Accept: */*" -H "Accept-Language: cs,sk;q=0.8,en-US;q=0.5,en;q=0.3" --compressed -H "Referer: https://www.youtube.com/" -H "Origin: https://www.youtube.com" -H "Connection: keep-alive" > J5.mpeg