IronFox is Firefox ESR-based, completely de-Googled, has zero telemetry, and comes pre-hardened for privacy.
IronFox is a fork of Divested Computing Group's Mull Browser, based on Mozilla Firefox. Our goal is to continue the legacy of Mull by providing a free and open source, privacy and security-oriented web browser for daily use.
Probably it just means the configuration defaults that set the search engine have been changed. Honestly, I haven't found a compelling Firefox fork that makes it worth it to put in risk the future of the Mozilla engine they are all based on. I almost feel that using one of the open source WebKit-based browsers out there instead might make more sense at that point. It's been 10+ years since Google moved over to Blink, after all.
About the English thing.. I have no idea, but you are right.