The issue appears to be due to a HTTP3 problem. It appears that a recent update to the browser triggers an infinite loop in the network thread that prevents any pages from loading, leaving the browser useless.
However, this is an issue that can be temporarily overcome.
In a forum thread entitled ‘Infinite loop in HTTP3 hangs socket’, one user recommended a workaround.
“If anyone need to fix it, please open ‘about:config’ in a new tab. Search : ‘network.http.http3.enabled’ change to false, then restart firefox”, they suggested.
It is possible that Firefox may face a challenge issuing a fix to users. “I hope the auto-updater can bypass http3, otherwise I’m not sure how it’s going to update to fix the issue”, one user in the thread commented.
“Our current suspicion is that a cloud provider or load balancer that fronts one of our own servers got an update that triggers an existing HTTP3 bug”, Gian-Carlo Pascutto, a security engineering manager at Mozilla, wrote.
“Telemetry was first implicated because it’s one of the first services a normal Firefox configuration will connect to, but presumably the bug will trigger with any other connection to such a server (so disabling telemetry is pointless). Our current plan is to disable HTTP3 to mitigate until we can locate the exact bug in the networking stack.”
In a statement to The Independent, Mozilla said: “Firefox has witnessed outages and we are sorry for that. We believe it’s fixed and a restart of Firefox should restore normal behaviour. We will provide more information shortly.”