The central role of browsers has long motivated us to build and improve Firefox in order to offer people an independent choice. The right way to win users is to build a better product, but shortcuts can be irresistible - and there’s a long history of companies leveraging their control of devices and operating systems to tilt the playing field in favor of their own browser. For example: making it harder for a user to download and use a different browser, ignoring or resetting a user’s default browser preference, restricting capabilities to the first-party browser, or requiring the use of the first-party browser engine for third-party browsers.

Source: Platform Tilt: Documenting the Uneven Playing Field for an Independent Browser Like Firefox - Open Policy & Advocacy