Well NSS has been stable for a long time and has a nice regression suite from what I have read. I dont see why updating the browser would break it.
I don't mean due to bugs in NSS, I'm sure they've done a great job. I mean because the actual library location itself has moved, or can no longer be found by the linker. Given that the official installer lets you install anywhere, it might well be a problem. I know it's broken Gaim for me before .