Randomly while browsing Firefox will stop responding for a few seconds and recover. This can happen a few times in a row while my hard drive works so furiously that other applications also slow down. I haven’t found a reliable way to reproduce the problem, but today I did get around to finding the bug report.
should be arriving soon that will fix this problem. In the meantime, if you’re affected you can try a workaround. [update] The update has arrived this morning.
In Firefox, click Edit->Preferences. In the Security section, uncheck the two boxes for attack site and forgery warnings. Close Firefox. Open your file browser to ~/.mozilla/firefox/[profile], where [profile] will be a short random string of characters. Delete any files with names starting with urlclassifier.
Be advised that this workaround will disable Firefox’s warnings for phishing and malicious websites. Re-enable the warnings when the update to the package xulrunner-1.9 arrives, which should fix the issue.
The problem is caused by Firefox’s urlclassifier database, which can get very large. Because the cache for this database is too small, there’s a lot of disk and CPU usage at certain times when accessing it.
I’ve done the workaround, but it’s hard to say whether it’s working because the problem comes and goes randomly.
[update] The update hasn’t fixed the problem for me. However, I’ve had only one brief random freeze, so maybe the issue has been minimized.