torbrowser logs lots of data to ~/.xsession-errors

I've noticed that TBB (on Tails, perhaps elsewhere) when loading some pages will log an excessive amount of data to ~/.xsession-errors

Sample:

[10-22 17:15:37] Torbutton INFO: SSC: Parent null for https://trac.torproject.org/projects/tor/newticket
[10-22 17:15:37] Torbutton INFO: SSC: Set cacheDomain to trac.torproject.org for https://trac.torproject.org/projects/tor/newticket
[10-22 17:15:39] Torbutton INFO: SSC: Parent trac.torproject.org for https://trac.torproject.org/projects/tor/chrome/common/draft.png
[10-22 17:15:39] Torbutton INFO: SSC: Set cacheDomain to trac.torproject.org for https://trac.torproject.org/projects/tor/chrome/common/draft.png
[10-22 17:16:17] Torbutton INFO: SSC: Parent trac.torproject.org for https://trac.torproject.org/projects/tor/chrome/common/topbar_gradient2.png
[10-22 17:16:17] Torbutton INFO: SSC: Set cacheDomain to trac.torproject.org for https://trac.torproject.org/projects/tor/chrome/common/topbar_gradient2.png
[10-22 17:16:22] Torbutton INFO: SSC: Parent null for https://trac.torproject.org/projects/tor/newticket
[10-22 17:16:22] Torbutton INFO: SSC: Set cacheDomain to trac.torproject.org for https://trac.torproject.org/projects/tor/newticket
[10-22 17:16:22] Torbutton INFO: SSC: Parent trac.torproject.org for https://trac.torproject.org/projects/tor/chrome/common/loading.gif
[10-22 17:16:22] Torbutton INFO: SSC: Set cacheDomain to trac.torproject.org for https://trac.torproject.org/projects/tor/chrome/common/loading.gif

This looks like a seriously bad bug:

amnesia@amnesia:~$ wc -l .xsession-errors 
140733 .xsession-errors

On a system not running Tails, I can imagine that this is a privacy disaster. It may just be my Tails system with TBB (31.2.0 (Tor Browser 4.0)) and it may be confined to Tails and Tails alone.

While writing this bug report the number of lines went up:

amnesia@amnesia:~$ wc -l .xsession-errors 
140749 .xsession-errors