NSPR, the Netscape Portable Runtime

mozilla/nsprpub/pr/src/md/os2/*
mozilla/nsprpub/pr/include/md/_os2.cfg
mozilla/nsprpub/pr/include/md/_os2.h

These are the base operating system services: threads, semaphores, file access, etc. This code seems stable; some OS/2 functions are not implemented, eg. the memory-mapped file routines. This has not been a problem in practice.

It would be worth reviewing the code; several small but serious bugs have cropped up over the past couple of months.

mozilla/nsprpub/lib/ds/plevent.c

This file defines a cross-platform event queue service, which is invoked from the XPCom library. If clicking on links in the browser stops working, someone's changed the event queue service. See Managing message queues.