A new console is opened whenever the browser restarts in debug mode, such as after installing an add-on. It should use the same console instead. This was introduced after the service was landed, in particular from bug 711692. It was added originally because it was suspected it would help a callback app in use error that happened intermittently, but it wasn't needed after all. The side effects were not all fully understood at the time of adding.
Created attachment 588806 [details] [diff] [review] Patch v1. This is where it was added by the way: https://bugzilla.mozilla.org/page.cgi?id=splinter.html&bug=711692&attachment=585742 The CreateProcessAsUserW call is not currently used but should be consistent with the CreateProcessW one.
Thanks for the review Jim. Pushed to inbound. http://hg.mozilla.org/integration/mozilla-inbound/rev/d0eed1fd4272