mastodon.ar.al is one of the many independent Mastodon servers you can use to participate in the fediverse.
This is my personal fediverse server.

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Aral Balkan

So the issue is this: when you carry out a form POST from Firefox, it disconnects any WebSocket connections that might exist.

WebKit and Chrome do not.

This feels like a bug to me. (Or at least, it should be brought in line with the behaviour of the other two browsers.)