Using Build ID: 2002082304 Somehow my Download Manager is loading a malformed moz-icon URL which is quite slow to resolve on my PC. I've trimmed the URL as much as I can while it still displays the bug. Note that no icon actually loads, normally for a really malformed URL a generic icon is displayed. Oh, and you can't actually display moz-icon: URLs in the browser (because the MIME type is wrong? a moz-icon: is image/icon but other icons are image/x-icon), so what I do is use DOM inspector to set it as the src of a XUL image.
This seems to be OK now.