See https://bugzilla.mozilla.org/show_bug.cgi?id=1062713#c30. We move messages around a lot, and each time we're allocating a new buffer, copying the data, and deleting the old buffer. It's not at all uncommon to have 32KB buffers, so this is really wasteful.

I already started looking at this in bug 1092010, so I'm just going to dupe it forward there.