By default, Firefox:
- Collects a bunch of telemetry data via several mechanisms and ships them to Mozilla HQ
- Provides Mozilla with remote code execution privileges on your machine via the shield (or normandy, or whatever they are calling it these days) mechanism, which can install and uninstall extensions and certificates, change browser settings, etc
- Uses Google as the default search engine, and search suggestions leak private data to Google
- Uses Google Location Services for their geolocation thingy, which - unsurprisingly - phones home to Google
- Ships closed source third party add-ons
- Comes with a bunch of "about:config" settings configured in sub-optimal ways, privacy wise - battery API enabled by default, accept all cookies by default and so on
Sure, Chrome is worse, but bringing that up that is like arguing that your pile of manure is better because it doesn't smell as bad: in the end, you are still arguing about shit.