This would be a
privacy option for Firefox, not the default. But yes, Tor introduces latency and reduces bandwidth. For traffic to the open Internet, traffic uses circuits through three relays: entry guard, middle and exit. So there are four hops between users and websites, instead of one. The Earth's circumference is about 40 thousand km. So the longest path is arguably ~20 thousand km. And rtt for that would be about 300-500 msec, according to my measurements.[0] It's only ~130 msec at lightspeed, but there are some copper links, plus switching time and caching.
So with four hops, rtt would at most be 1200-2000 msec, if every hop were the maximum length. In practice, rtt for Tor is at most half that, and often even less. But latency is actually good if your goal is anonymity. Because it reduces the accuracy of traffic analysis.
With traditional onion sites, there are two three-relay circuits, one for the user and one for the site, plus a rendezvous relay. So rtt is much greater. However, sites can opt for one-relay circuits, sacrificing anonymity, so overall rtt isn't that bad.
Bandwidth is also reduced with Tor. Increased latency is part of that. But also, many relays have low-bandwidth uplinks, especially ones that people run at home. The Tor client does pick faster relays, but there's a tradeoff, in that doing so reduces anonymity. Increased investment in high-bandwidth relays would help a lot.
Also, with more relays, it would be workable to implement multipath circuits. Especially for onion sites, where precious exit relays aren't needed. Using MPTCP, I managed ~50 Mbps throughput for bbcp transfers between onion sites (with gigabit uplinks).[1] I was getting ~36 subflows per tcp connection.
0) https://www.ivpn.net/privacy-guides/how-to-verify-physical-l...
1) https://ipfs.io/ipfs/QmUDV2KHrAgs84oUc7z9zQmZ3whx1NB6YDPv8ZR...