[ohgodplsno]

Indeed! And that is perfectly fine. The employer can dispense you from your préavis de licenciement, especially if it's a single person being fired. https://www.service-public.fr/particuliers/vosdroits/F24660

However, any firing must be notified of an entretien préalable de licenciement by letter (can be given directly). This is usually a week after, to grant the employee time to prepare (and to eventually be helped by employee representatives). Then, after this, the employer has to give at least 48 hours before doing anything. This gets even worse in the case of a massive layoff like Coinbase's for economical reasons, the company is obligated to have meetings with the employee representatives, at the very least twice spaced by 15 days. For a company the size of Coinbase, the CSE has 2-4 months to answer and can ask for proof that the company is, indeed in financial troubles, having them open their books. https://entreprendre.service-public.fr/vosdroits/F24648

So, in practice, while quick firings are possible for individual cases, massive layoffs like that do not happen over a single day.