Maybe use sockstrace in automated tests for proxy leak detection

@JeremyRand demo'd sockstrace's capabilities to me last week and it looks like a promising avenue to explore for proxy leak detection. We should consider developing a suite of tests targeting the various browser technologies (e.g. websockets, webrtc, etc) and verify they don't bypass Firefox's proxy. Any tests should also be developed to be upliftable so they can run in and augment Mozilla's nightly test automation so issues can be found early during the rapid-release cycle.

@ma1 could you reply with a short-list of areas which we should verify dont leak?

@JeremyRand can you reply with link to the proejct's repo and brief (i.e. one to two sentence) overview of what sockstrace is what it does and how it works for future us?