Firefox has an "official" add-on called Multi-Account Containers. This isolates website state (cookies etc.) but not history/settings/extensions. Alternatively

Firefox has an "official" add-on called Multi-Account Containers. This isolates website state (cookies etc.) but not history/settings/extensions. Alternatively, you can start Firefox with `--no-remote -ProfileManager` flags to get a totally separate instance, like Chrome does. Personally, I use Multi-Account Containers together with the Temporary Containers add-on, to by default get a fresh cookie jar for each new tab, but I do have some websites tied to a named container for session persistence.