1) Run nightly
2) Install the addon: https://builder.addons.mozilla.org/addon/1023834/latest/
3) User the browser and dump some profiles.
The browser should hang shortly after.
Created attachment 584095 [details] [diff] [review]
So the reason that this happens is that TimeStamp::Now() tries to hold a critical section, and if the mainthread has already acquired that lock and is currently paused, a deadlock occurs.
A simple fix is to grab the timestamp before pausing the main thread.