A highly portable 32-bit web browser with minimal requirements (a graphics mode, a mouse pointer and a TCP/IP stack). With a cross-platform and endian-neutral code base that allows it to be compiled even with older compilers.
Basically the same idea as TenFourFox, but cross-platform. It would require quite a bit of backporting work, though. Pretty much the only two remaining open source browser code bases are Firefox and Chromium, both of which use modern language features (and in the case of Firefox even require a Rust compiler), which aren't available in older environments.