unicorn This is some local issue because:
a) firefox binaries exist for both 8.0 2023Q2 and 9.0 2023Q2.
b) for 10.0 2023Q2, binaries have been built from the 2023Q2 sources for the ARM and other architectures.
First, check your memory: memtest86 or [memtest+)(https://memtest.org/).
Select all the tests and run them for a day or so.
Next, try a clean rebuild: get rid of the work and build directories, etc. Keep an eye on the CPU temperature while the build is going on.
Or, if you don't want to compile stuff, you could try the SmartOS binary packages for NetBSD. It's built for 10.0-BETA.
Note that if you want to switch back to NetBSD's official repo., you'll have to remove all the SmartOS packages, remove the package databases, etc.