Most of the attacks target Windows and Mac, so one is already protected by using Linux.

As regarding effectiveness of firejail, then it relies on Linux container protection which is quite good given that many providers use that to run untrusted code.

However, the problem with firejail or similar tools is that that try to integrate with GUI and that makes the attack surface vastly bigger. To protect against highly sophisticated attacks something like Qubes OS should be used with explicit whitelisting of domains to connect.