Then you must not have read the linked article, which mentions three companies that have done just that.
Roaming charges made an unwelcome reappearance for UK mobile users heading to mainland Europe after Brexit. EE, Three and Vodafone were all quick to reintroduce the daily or monthly charges to use their mobiles while in the EU – which typically add £2 a day.
Are you sure you don’t have some other software updating Firefox in the background?
Normally this only happens on Linux when your package manager updates Firefox while it’s running, and on Windows that doesn’t happen because Firefox updates itself only when you (re)start it.