If you are using Firefox 3 Beta, and you are having the issue that firefox will lock up with 100% (or nearly so) disk access semi-randomly for a few seconds, this is the solution
This issue relates to Firefox's new phishing/malicious website protection feature. The problem is that Firefox stores a very large list of websites in the profiles folder which it matches against URLs to tell whether or not they are suspected of phishing or malicious activity. This list can be at lease 50MB in size. However, it seems that Firefox does not cache this in RAM (or if it does, not for long), so every time it needs to be accessed, Firefox may lock up while it reads it. My suspicion is that this was done so that Firefox could operate with as small a memory footprint as possible, which is a good idea, but for machines with enough memory, the freezing is unacceptable.
The Fix, Itself.
In order to fix this issue, open Firefox, and in the address bar, type:
about:config
and hit enter. You will come to a page that asks you if you're sure that you want to proceed. Click the "I'll be careful, I promise button" (because you will, won't you?)
In the "Filter:" box, type:
urlclassifier
and hit enter. You are looking for an entry in the results with the name:
urlclassifier.updatecachemax
If it exists, then right click on its entry, and click on the "modify button". Enter the value, in bytes, that you want it to cache. For machines with enough memory, "104857600" (without the quotes. This is equal to 100 MB) is recommended, or -1, which sets it to no limit.
If it does not exist, right click anywhere and select "new", then select "integer". Enter "urlclassifier.updatecachemax" (without the quotes) as the name, and enter the value, in bytes, that you want it to cache. See above for recommended values.
Once you've done this, restart firefox, the changes will apply, and you should be freeze free.
