Ubuntu: .xsession-errors ate 37.1 GiB of disk space: What is causing that?

Ubuntu recently informed me that I used up all disk space and need to free some more.

After few hours spent looking for guilty party, I found out that my .xsession-errors file size is 37.1 GiB!

I haven't read it completely (thank GNU for less and its ability to read only parts of files!), but most common errors appear to be

 (npviewer.bin:2918): Gdk-WARNING **: XID collision, trouble ahead

/usr/share/themes/NOX/gtk-2.0/gtkrc:233: Murrine configuration option "gradients" is no longer supported and will be ignored.
[0x7fc5d4023518] pulse audio output: No. of Audio Channels: 2
*** NSPlugin Viewer  *** WARNING: unhandled variable 18 (<unknown variable>) in NPN_GetValue()

For comparison old .xsession-errors was around 10 KiB.

This is in my opinion very strange.

My question is : How do I found out what's causing such behavior and how to stop it?

The npviewer.bin and NSPlugin Viewer lines come from NSpluginwrapper, which lets you use 32-bit browser plugins in a 64-bit browser. The first line leads to Ubuntu bug 401823 (no fix for Lucid). The second line leads to Ubuntu bug 592492 (no fix for Lucid).

As a workaround, you could:

• run a 32-bit browser. (At some point, I got into the habit of running an i386 firefox on my amd64 machine, because it took less than half the memory!)

• try the amd64 flash player. It's not 100% complete, but it might work for the content you habitually browse.

• discard the output of NSPluginWrapper. This may hide important error messages, of course. Here's one way to do it (untested, run as root):

  dpkg-divert --add --local --rename --divert /usr/bin/nspluginwrapper.bin /usr/bin/nspluginwrapper
  echo '#!/bin/sh' >/usr/bin/nspluginwrapper
  echo 'exec /usr/bin/nspluginwrapper.bin "$@" 2>/dev/null >/dev/null' >>/usr/bin/nspluginwrapper
  chmod 755 /usr/bin/nspluginwrapper
  

The Murrine line could come from any GTK application. It's discussed in Ubuntu bug 518325 (status unclear).

The No. of Audio Channels could come from any sound-producing application. There doesn't seem to be an Ubuntu bug about it, though this is debugging output that shouldn't have been included in a release. This message seems to come from the VLC pulseaudio plugin, so maybe the culprit is the VLC browser plugin all along (though I don't know why it would run in NSPluginwrapper).