While I agree that Chrom(e|ium) sandboxing and the backing of Google's security teams make it a security leader, I'm torn between Chrome/Chromium and Firefox because of privacy considerations. For example, privacytools.io recommends Firefox for reasons such as its tweak-ability, and because WebRTC can be disabled so that when using a VPN, the originating IP isn't leaked. Other tweaks include the ability to disable both the disclosure of battery status and clipboard events.
I'd love to get your opinion on the trade-offs between the current un-sandboxed version of Firefox, and Chrome/Chromium.
Edit: Also, thegrugq[0] recommends against using Safari, but makes no mention of Firefox. While Safari is not atop my list of privacy or security focussed browsers, I'm somewhat surprised to see if specifically mentioned as one to be avoided. If you agree with him, why is that? In my view, it's not terrible because it doesn't support WebRTC, a user can disable plugins, and because WebGL can also be disabled. While it can't run HTTPS everywhere nor a random user agent spoofer, JSB5 seems pretty good for a javascript blocker and uBlock (while no longer under development) still works rather well.
[0] https://gist.github.com/grugq/353b6fc9b094d5700c70