Just tried a native firefox-69.0.1 binary on NetBSD/amd64 9.0_BETA, and so far the stability issues I had with the firefox NetBSD/amd64 8 binaries (on 8 & 9) seem to have completely gone.
I can consistently load maps.google.com, I no longer sometimes see odd delays when fetching pages (including from localhost). Colour me happy :-p David