I can't find a good answer on the plain old boring Internet, so I'll try Mastodon.
Why do I get faster download speeds with wget compared to Firefox? No tricks; just download [some big file] and watching download speed: 100kbps-ish in Firefox. Same download with wget, 1Mbps, peak 2Mbps.
I've noticed this over the past couple of years, chalked it up to randomness. But it seems reliable.