SO, I guess that is going to be used on all my firefox runs.
To be serious, this has introduced me to sandboxing on BSD via pledge [0] and comparisons against Linux seccomp [1] - thank you!
[0] https://news.ycombinator.com/item?id=17289654
[1] https://kristaps.bsd.lv/devsecflops/ (submission by same poster at https://news.ycombinator.com/item?id=44264021)
SO, I guess that is going to be used on all my firefox runs.