The Chromium engine which Google Chrome relies on (as well as Opera) has a sandbox container for starters, but Firefox may also have such capabilities.
Site Isolation can be a beneficial defense against web-based Spectre exploitation being carried out by locally-executing JavaScript (loaded by the browser and from a website you're visiting). It works by spawning a new process per tab document with the sandbox container, and thus if exploitation of a vulnerability which works like Spectre was deployed, data exposure would be minimal compared to without the Site Isolation feature enabled (since there'd be less memory compromised for unauthorised read access).
The other Chromium sandbox containment features involve process mitigation policies to make exploitation more difficult. An example of a process mitigation policy would be Address Space Layout Randomization, Data Execution Prevention, Control Flow Guard or disabling of win32k system calls.
I once looked into the differences between security with Google Chrome and Firefox regarding banking malware (specifically form-grabbing and WebInject installation techniques) and concluded that Google Chrome was more of a difficult target in comparison to Firefox, but this is only because Google Chrome utilizes AppContainer support by default. From what I have seen, most attackers rely on DLL injection over a "file-less" approach (like code-cave/shell-code) when it comes to locally-based banking malware for form-grabbing and WebInject via compromising the memory of the browser process... And while Google Chrome isn't that much of a strong target against it, you at-least have to do more steps like change security rights on the module being injected for it to be seen as "Trusted" and allowed to be loaded by the Google Chrome processes, and this wasn't the case with Firefox last time I checked.
Mozilla Firefox introduced a new feature recently for isolating Facebook if I remember correctly; I may be mixed up with another browser.
I'm a fan of Mozilla Firefox because I feel they care more for privacy compared to Google. Feedback on Firefox is usually quite good from what I've seen, and I used to be a user myself... I don't recall it ever causing me much trouble.
You can enhance your protection on either browsers through using an ad-blocker to help fight against malvertising and disabling auto-play content (e.g. Adobe Flash). If you wanted to, you could use a Virtual Private Network (VPN) to help protect against IP address exposure and even a third-party sandbox (which will work differently to how browser sandbox containers work, but bear in mind, they usually aren't compatible with each other).
The short answer is that both Google Chrome and Firefox are good choices. I think that you should use which ever one makes you feel more comfortable with using, and as always, don't be click-happy and make good choices.
Aside from being careful of your general browsing habits for website viewing and security add-on usage, remember to stay safe in terms of what data you give out whilst you're on the internet. You should be careful of who you give your data to and where. This is one of the most important things to remember. As an example, if you go around on the internet sharing your e-mail address with strangers or signing up to loads of junk, you're going to end up being repaid with an increase of malicious/spam mail due to e-mail scrapers and dodgy mailing lists/third-party data sharing... misbehaving when it comes to data sharing will increase your attack vector.