Comment by scorpioxy

For a while, I used a firefox extension called "Temporary Containers" which would, as the name implies, create a temporary container for each site you visit. Combined with specifying some custom rules for ones you want to open in a specific container, that was a very convenient setup. But the extension at some point corrupted my firefox profile and has been unmaintained for a while so I didn't try again. I am not sure what happened and it may have been the combination of extensions that was the cause of that. Sadly, the author passed away, if I remember correctly, and it's been difficult to find maintainers for the project so I gave up on that.

You can still install that extension but from the reported issues the functionality and bugs were increasing with every new firefox version. And obviously that setup only helped with the cookie aspects and not necessarily any security issues from javascript and so on.