Icecat on Mobian on PinePhone

[wibble]

IIRC the gentoo build process does an early test for >=4GB RAM before attempting to compile the major browsers, and even then you'll run into heavy swap use. You can probably either build natively with something like an 8GB Pi4, or crosscompile on a more capable x86_64 machine which is almost certainly how the mobian packages are built. That should allow you to build a package with all the correct dependencies to run.
https://wiki.debian.org/CrossCompiling