The server at s.yimg.com supplies many important components of Yahoo pages. If you block it completely, you'll experience a lot of breakage. How often does this problem occur? Next time, copy your unsaved comment to a safe place (e.g., a Notepad document) and reload the page bypassing the cache. You can do that using Ctrl+Shift+r or holding the Shift key while clicking the reload arrow in the address bar. If you get back to where you were and paste the comment and try to submit it, any improvement?