Genuinely asking as I've tracked numerous CVEs in Chrome and Firefox. Also I don't have much experience with Rust, so I don't represent the RIIR community!
> Why build a new browser in C++ when safer and more modern languages are available?
> Ladybird started as a component of the SerenityOS hobby project, which only allows C++. The choice of language was not so much a technical decision, but more one of personal convenience. Andreas was most comfortable with C++ when creating SerenityOS, and now we have almost half a million lines of modern C++ to maintain.
> However, now that Ladybird has forked and become its own independent project, all constraints previously imposed by SerenityOS are no longer in effect.
> We have evaluated a number of alternatives, and will begin incremental adoption of Swift as a successor language, once Swift version 6 is released. (More background.)
One other interesting tidbit is that the development team was excited to try Rust, but in practice disliked it, and the reverse was true for Swift.