User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.0.0 Safari/537.36

Steps to reproduce:

I have a server that is RFC 8441 compliant and offers only h2. The server is available in a git repo, in order to run it you have to follow these steps on a linux machine or wsl2 :

Install SDKMAN! from https://sdkman.io/install (this is needed only to install with ease other apps like java and maven; one can install them by other means)

sdk install java 17.0.3-tem
sdk install maven
git clone https://github.com/lachlan-roberts/websocket-http2-embedded-example
cd websocket-http2-embedded-example

Because FF has issues with self signed certificates and this repo uses one with CN=localhost it has to be replaced with another one otherwise FF won't load the main page - so issue another with a different CN:

openssl req -newkey rsa:2048 -nodes -keyout key.pem -x509 -days 3650 -out certificate.pem

make sure you will have : Common Name (e.g. server FQDN or YOUR name) []:demo

openssl pkcs12 -inkey key.pem -in certificate.pem -export -out certificate.p12

use 'storepwd' when Enter Import Password: is prompted

cp certificate.p12 src/main/resources/keystore.p12

Add in /etc/hosts an entry for 'demo' and the local IP.

Now run the server

mvn compile exec:java -Dexec.mainClass="org.example.Main"

Open https://demo:8443 in FF and fill the URI field from the main page with wss://demo:8443 and press Join button (this will try to open a wss session)

Actual results:

The websocket session does not open, see attached screen shots (ff-wss.png). In the console there is the following error: Firefox can’t establish a connection to the server at wss://demo:8443/

User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:101.0) Gecko/20100101 Firefox/101.0

Expected results:

The websocket session should open as it does when doing the same with Chrome 102.0.5005.115

User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.0.0 Safari/537.36)

The Bugbug bot thinks this bug should belong to the 'Core::Networking: WebSockets' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

This can also be tested with a public server at https://libwebsockets.org/testserver/
WSS/H2 badge does no show if opened with FF.

Successfully replicated.
Websockets over h2 were disabled as per this.

Depends on D165274

https://hg.mozilla.org/mozilla-central/rev/2bfa261943a5
https://hg.mozilla.org/mozilla-central/rev/6c7e9cf2f986