Hello !
Do you know of a plugin that would allow me to authorize certain websites only (whitelist) ?
Important note: when I visit a website that is in the whitelist, all requests made on other domains (from this whitelisted website) must be authorized. And it seems whitelist plugins I found filter without this behavior.
Thanks 
I think you should be able to configure AdGuard to do this for you. You could set a default rule to block all web sites and manage the allowed websites through the Allowlist.
Thanks for sharing the AdGuard approach. For anyone looking for stricter control, another option might be combining a whitelist extension with Firefox’s built-in protections or a DNS-level filtering solution. In my experience, the challenge is usually handling third-party resources that trusted sites depend on, so maintaining the allowlist can require some ongoing adjustments. Has anyone found a setup that balances security with minimal maintenance?