Apple hasn’t announced any rule changes. The correlated activity from Google and Mozilla could suggest that they’re expecting Apple to drop its restrictions on third-party browser engines in the near future, or the companies could simply be hedging their bets. Regulatory pressure from multiple governments is pushing Apple in the direction of loosening many of its App Store restrictions, including (begrudgingly) accepting third-party payment services and sideloading of apps and third-party app stores.

Source: Google and Mozilla are working on iOS browsers that break current App Store rules

This might be just enough to change everything about mobile platforms