The Portable Freeware Collection Forums

Just a quick mention of multi-platform Nyxt browser for what is worth -- I don't expect it to become natively portable anytime soon, since it's advertised as a "browser for power users", who can potentially bend it to their wills as they see fit...

Nyxt: the hacker's power-browser. Out of the box Nyxt ships with tens of features that allow you to quickly analyze, navigate, and extract information from the Internet. Plus, Nyxt is fully hackable- all of its source code can be introspected, modified, and tweaked to your exact specification.

Nyxt [nýkst] is a keyboard-driven web browser designed for power users.

Nyxt current stable release is v2.2.4 (downloads and changelogs at https://github.com/atlas-engineer/nyxt/releases).