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How to diagnose the cause of Firefox freezing/hanging on Mac

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How to diagnose the cause of Firefox freezing/hanging on Mac

I found an issue, but I need help diagnosing the exact steps to re-create the issue suitable for a bug report. In this case, Firefox 16/17 is freezing (spinning beach ball, 100% CPU load on one of the cores) upon start-up when trying to restore a set of tabs. If I kill FF 16/17 then launch FF 18/19/20 (Beta/Aurora/Nightly) everything loads fine.

I've used Safe Mode to turn off extensions and plugins. I've also tried resetting the browser. But no luck. I also tried putting all of the tabs into unloaded tab groups (so that only the default "New Tab" tab opens upon startup). Surprisingly, even a blank "New Tab" didn't prevent the browser from freezing.

So, does anyone know of some way to get FF to verbosely generate debug output on the console (or perform some other tracing method) in order to deduce the cause?