Disable DNS over HTTPS in Firefox
Mozilla recently changed Firefox's default behavior so that all United States users are using technology called DNS-over-HTTPS, which stuffs your DNS queries into an HTTPS request, which then spits back the IP to connect to. On its surface it's supposed to be "more secure", but the default DoH provider is Cloudflare. This should be alarming to anyone who considers centralization a threat. The effect of this is that all Firefox DNS traffic will be routed through Cloudflare, creating a funnel of information to a single provider.
Cloudflare uses Google captchas and other analytics. Mozilla has also been gathering "anonymous browsing data" through their Studies platform. The only real reason to gather this data is to sell it; very little of this data is useful for the Studies program, and using hot/cold or A/B testing for determining features is poor software design philosophy. As such, I recommend disabling DNS over HTTPS, or running your own Trusted Recursive Resolver, if you're going to stick with Firefox.