I'm another one having trouble expanding comments on my two accounts that are using beta features. It's extremely laggy - as in it kind of never works ever - and refreshing the page doesn't help, no matter what. If I switch to an account without beta features, then expanding works fine. No error messages, it just says "loading" forever.

For clarification:

- I'm using up-to-date Firefox on a Mac, ljlogin, Adblock Plus, and Greasemonkey (but my only script is for LJ and I don't think I have it turned on anyway), and I never had this problem before turning on beta features yesterday.

- I've actually only been on site skin pages so far, so I can't tell you if it happens on custom comment pages.

Hope this helps!