The first time we spawn a process using NSPR on Unix-ish systems, it spawns a wait() loop thread that reaps any child processes as soon as they exit. That has the side-effect of making it impossible for other IPC code to wait on its own child processes, and results in errors like: [Parent 14896] WARNING: waitpid failed pid:14967 errno:10: file /home/kris/code/mozilla-central/ipc/chromium/src/base/process_util_posix.cc, line 276 It seems mostly harmless in cases like this, but it can also cause more serious problems (e.g., 1370027), especially for code that needs to be able to reliably check exit statuses.