Use Firefox Focus ... especially on mobile. Open such a website in Focus, just accept cookies and the hit the trash button to delete it all. Many sites are just

Use Firefox Focus ... especially on mobile. Open such a website in Focus, just accept cookies and the hit the trash button to delete it all. Many sites are just trying to be compliant to law and it wouldn't matter to them if you trash their cookies. For those nefarious ones that store unnecessary cookies, don't give them room and just trash it all.