GraphQL Subscriptions not working on Firefox - Error 400 bad Request

Question

I have a Frontend app that is built in React and it is connected to a GraphQL backend using Apollo Client.

Queries and Mutations are working fine in all browsers, but I have an issue with the Subscriptions. On Google Chrome and Safari are working fine, but on Firefox I get always this two errors:

Firefox can’t establish a connection to the server at wss://my-backend.net/graphql-ws

GET wss://my-backend.net/graphql-ws - Error 400 Bad Request

And the wsLink in the Frontend looks like follows:

import { WebSocketLink } from '@apollo/client/link/ws';

        const wsLink = new WebSocketLink({
            uri: process.env.REACT_APP_WEBSOCKET_URL || '',
            options: {
                reconnect: true,
                reconnectionAttempts: getReconnectAttempts(process.env.REACT_APP_WEBSOCKET_RECONNECTION_ATTEMPTS),
                connectionParams: () => ({
                    Authorization: authStore.token,
                    'Ocp-Apim-Subscription-Key': process.env.REACT_APP_SUBSCRIPTION_TOKEN as string,
                }),
            },
        });

Does anyone have any idea of what is happening here? Why is it working well on Chrome and not on Firefox?

Thank you all in advance.