Like others have said, uBlock Origin ( or solid alternative; uMatrix, etc ) at this point is a prerequisite for any browser.
I am not testing something that puts me in danger and throws me into the festering garbage dumpster that internet is these days without it. It's like testing a car that doesn't have brakes yet.
Pi-hole at the DNS level, ublock origin and fingerprint protection at the browser level.
If the latter two are missing because I'm testing a beta browser which is very likely to a) deliver them and b) help defend against a chrome monoculture, I feel alright about sshing into a VPS to update pi-hole and then taking it for a spin.
Tell me how am I supposed to test add-ons on this Firefox as a developer before the release then.
Edit : And again, most of my work if not all related to Firefox, I do on the Nightly build. I expect things to break, but this preview ( of which there have been builds for a while already ) is a non-starter.