http://people.mozilla.com/~bgirard/cleopatra/#report=5e274cf239170180d9f19367c2ef2443b3438d2a I don't understand what's going on in this profile, but Firefox is sitting using 100% of one CPU with all but two bugzilla tabs closed. That seems pretty bad! Nightly built from http://hg.mozilla.org/mozilla-central/rev/b94e996b05fd Mac OS 10.8.
You don't have js profiling enable (you should) but I'm going to guess that it's Firefox Sync (or maybe FHR but I think it got fixed) that's spinning the event loop. It looks like your main thread is mostly idle waiting on events with a nested event loop. Your CPU usage is likely coming from another thread. I suggest using Instruments.
I've restarted my browser (sorry), but the "js profiling" checkbox is checked. Is there anything else I need to do to get that working? If it happens again I'll use instruments.
> Firefox is sitting using 100% of one CPU How did you measure this?
(In reply to Steven Michaud from comment #3) > > Firefox is sitting using 100% of one CPU > > How did you measure this? Activity monitor.