An open-source fork of the Firefox web browsers, with a strong(er) focus on privacy and security. Basically disables all telemetry and most of the slightly questionable decisions that Mozilla have made over the years, either by stripping them out completely or relegating them to user-controlled settings (such as session restore). Also comes bundled with an ad-blocker and a few privacy settings enabled by default. Claims to keep up-to-date with the latest Firefox release, with a 1-3 day lag to ensure nothing slips through.
Not worth the switch right now (it obviously also disables features like Firefox Sync) but useful to remember in case Mozilla goes off the deep end 😉