I think Firefox's "Temporary Containers" add-on in Automatic Mode is vital - it'll load every new domain into a sandboxed container which automatically drops all cookies & local storage when it's closed.
The only other relevant Add-ons I use are uBlock Origin & uBlock Matrix.
I do also use ghacks-user.js to add restrictions to the "user.js" in my Firefox profile directory, but that requires extra effort to periodically run before starting Firefox, so won't be suitable for everyone.
To deal with particular sites which don't like such restrictions, I use a completely separate Firefox profile.
E.g. I have a profile exclusively for work use of Office365 - the only add-on installed in that is uBlock Origin, and I don't use ghacks-user.js - but I do have to be careful not to visit any non-work non-Office365 URLs in that profile.