Firefox Nightly/Beta enables QUIC and HTTP/3 support by default

The official Mozilla blog announced that support for QUIC and HTTP/3 is currently enabled by default in Firefox Nightly and Firefox Beta, and it is planned to start enabling it in Firefox 88 for the stable version. HTTP/3 will be enabled by default before the end of May.

This means that if a web server (such as Google or Facebook) provides HTTP/3, Firefox Nightly and Firefox Beta will automatically try to use HTTP/3 when visiting these websites.

The web server can indicate that it supports HTTP/3 by using the Alt-Svc response header or by using the HTTP/3 support of HTTPS DNS record. Both the client and the server must support the same draft version of QUIC and HTTP/3 to connect to each other.


For example, Firefox currently supports drafts 27 to 32 of the specification, so the server must report support for one of these versions (such as “h3-32”) in the Alt-Svc or HTTPS record so that Firefox can try to use QUIC and HTTP/3 to connect. When visiting this kind of website, viewing the network request information in Dev Tools should show the Alt-Svc header and also show that HTTP/3 is used.

HTTP/3 is a new version of the HTTP protocol based on QUIC. Compared with HTTP/2, HTTP/3 has three main performance improvements:
  • Because it is based on UDP it takes less time to connect;
  • It does not have head of line blocking, where delays in delivering packets cause an entire connection to be delayed; and
  • It is better able to detect and repair packet loss.

QUIC also provides connection migration and other functions that can improve performance and reliability.