Steps to reproduce:

On a Win 10 laptop, when connecting to a commuter train WiFI, the following page:
https://myacewifi.com/en/connecttoweb
is automatically is visited by the default browser (Firefox).

Actual results:

The page loads, I provide my information, and then the laptop has network connectivity. However, Firefox then displays:
"[2000] Establishing a connection to the MQTT broker failed: TLS error [UNKNOWN:1]: Unknown error. 500 Server Error" at this point the URL is still the same as the one listed above.

Expected results:

When using Chrome as the default browser, instead of the 500 error, a page that says "you are now connected..." appears.

According to the sumo article [1], it seems to be caused by Firefox's attempt to use websockets over HTTP/2.

[1] https://support.mozilla.org/en-US/questions/1324001