This is caused by the WebContent process making a syscall not allowed by the sandbox.
rdar://problem/65897905
Created attachment 404855 [details] Patch
Comment on attachment 404855 [details] Patch r=me
Comment on attachment 404855 [details] Patch Thanks for reviewing!
Committed r264678: <https://trac.webkit.org/changeset/264678> All reviewed patches have been landed. Closing bug and clearing flags on attachment 404855 [details].