Chromium used to have better sandboxing, but since Firefox’s Quantum Update (Electrolysis), they’re almost identical in that regard.

If I remember correctly, they only start behaving differently with more than 8 tabs open. Chromium will continue to sandbox each tab separately (unless they’re from the same domain), whereas Firefox starts grouping multiple tabs into the same process for better performance and lower resource usage.

And well, personally I also think, it makes sense to look at more than just the browser itself.

Firefox has a much better track record with malicious add-ons and it blocks most tracking scripts, which will also include most online ads, which are a great way to distribute malware.

And if you’re using Chrome Sync, your data lands in decryptable form on Google’s servers, making it vulnerable to leaks and directly available to US intelligence services, who might use it for spear phishing attacks.

So, like, if the goal is to use the browser with which you get hacked less, I doubt Chromium wins that one.