It is almost impossible to use Gmail (mail.google.com) in Firefox. There are no problems in Chrome on the same machine.
In the browser developer console / Network tab I see some requests are without responses (zero bytes responses). Some with SSL_ERROR_BAD_MAC_ALERT
GMail app constantly shows yellow warning: "Ups... the system encountered a problem. Retrying in ..." . "Retry now" link doesn't help.
Similar errors discussed recently: https://community.sophos.com/sophos-central/f/discussions/133650/ssl_error_bad_mac_alert-pr_end_of_file_error
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