While using the latest nightly on a Ubuntu 10.10 (64bit) machine I noticed that the first time it syncs it can lock up my browser for several minutes. It happens a few seconds into having set up my existing account. The firefox-bin process stays at 100% cpu during this whole time and I am unable to switch tabs, use the location bar, or access any of the menus. Steps: 1. Set up Sync with an existing, rich account 2. Browse around for a little bit. Check out about:sync-log for example Expected: I can browse around normally Actual: During the Sync'ing process the browser can lock and become unusable. I'm assuming that depending on how rich your profile, history, bookmarks, etc... information is, this can take minutes, which in my case it does. Meanwhile the browser locks up. Reproducible: Always

A total lock up for several *minutes* definitely isn't expected, though a first sync would involve a lot of crypto and that would keep Firefox pretty busy for a while. The UI would be unresponsive due to a) an AES key being generated from your passphrase via PBKDF2 with 4096 iterations, b) an RSA key pair generated, c) lots of objects being en/decrypted, and d) all of that on the main thread due to the backout of bug 570619. We are going to put crypto back on a thread (bug 608156) and we're also going to get rid of the RSA layer (bug 603489). That should alleviate most of what you're seeing, especially if what you're witnessing only happens with recent nightlies (since the backout of bug 570619).

Probably a dupe of bug 606062, actually...

Hard to say until the crypto stuff is moved off of the main thread. Let's block on this and not dupe it, until some of the dependencies are resolved.

I can't repro this on current nightlies, even with very large profiles. Juan, if you're still seeing this, please renominate.

With the latest nightly, 2/01, I no longer experience a lock up. The CPU usage goes up, but I can interact with the browser without any noticeable problems.