Bugzilla has the tracking bug 1717203 [1]. When [2] and [3] are landed
the trunk tree of Firefox (https://hg.mozilla.org/mozilla-central/)
should build without patches.
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1717203
[2] https://bugzilla.mozilla.org/show_bug.cgi?id=1731773
[3]
As explained here: https://discourse.ubuntu.com/t/feature-freeze-
exception-seeding-the-official-firefox-snap-in-ubuntu-desktop/24210,
we're moving to a snap package for firefox.
The good news is, that snap is based on core20, which supports riscv64.
There will probably be build dependencies
