Comment 1 for bug 311622

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.3) Gecko/2008092417 Firefox/3.0.3

Am having exact same issue. I had set Firefox to clear private data at exit without asking and I thought it was a hang-on-exit problem at first. I followed the standard diagnostic and found that Firefox, as well as my entire operating system (XP SP3), froze for several minutes once I cleared the private data. The same thing happens when I clear the cache.

Steps to reproduce:
1. Tools -> Options -> Privacy
2. Select "Always clear private data when I close Firefox"
3. Make sure "Ask me before clearing private data" is not selected.
4. Close browser by pressing "X"

or

1 Tools -> Options -> Privacy
2. Hit "Clear Private Data now"

or

1. Tools -> Options -> Advanced -> Network
2. Under the "Offline File Storage" section, press "Clear now" to clear the cache.

Expected Results: whatever offline storage is deleted instantly.
Actual Results: Firefox hangs, entire operating system resources are consumed for up to four minutes. Firefox will eventually close, but the system is deadlocked until it does.