Same problem but with French equivalent SNCF (sncf-connect.com). I just checked and can confirm nothing has changed. You cannot use up-to-date Firefox on Linux to access the main booking site for French rail tickets.

    Access is temporarily restricted

    We detected unusual activity from your device or network.

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    -Rapid taps or clicks
    -JavaScript disabled or not working
    -Automated (bot) activity on your network (IP X.X.X.X)
    -Use of developer or inspection tools