I'm using Firefox 3.5.3, trying to view questions like this one.
Clicking the link makes Firefox freeze (can't even use other tabs), and attempts to answer or edit answers periodically hangs. My internet connection is a 1.5 MB download - it's not like I'm trying to check questions on dialup...
I believe the periodic hangs while answering (or editing answers) is likely due to the AJAX calls to provide the banner, altering the user that the question has been closed, or someone posted an answer while the current user was typing theirs.
IME, the behavior turns up when dealing with text that has a lot of code formatting in it.
I'll try to add more examples as I come across them: