"QUIC is a key element of HTTP/3, since it provides the foundations for its main features. Built on top of UDP, QUIC attempts to solve the major issues experienced when using the TCP protocol, i.e., connection-establishment latency and multi-stream handling in the presence of packet loss.
...For several years, Google has been using QUIC for its own services, including search, YouTube, and others, and also supported it in Chrome. For a while, Chrome was the only way to use QUIC when communicating with Google services supporting it. Recently, Mozilla added support for HTTP/3 in Firefox 72, too, although still experimentally. The command-line tool curl also added support for HTTP/3 in version 7.66.0, along with many additional features. Server-side, HTTP/3 is supported by LightSpeed and Nginx."