You have used '/home/user/.local/.share/trash/files/firefox' as the path
'local' is a hidden directory, so it's named '.local' (note the dot)
directory 'share' located within '.local' is NOT a hidden directory
also: it's 'Trash' and not 'trash'
simply remove the dot before 'share' in the pathname, correct 'Trash' and try deleting
/home/user/.local/share/Trash/files/firefox
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