How to regain some LJ functionality?

[pebblerocker]

I can't comment on LJ except on certain journals. The comment pages I can't use are the ones with the sort of speech bubble thing that expands into a box with pale blue all around it. Some journals and communities use a different comment box, the old sort, and I can use that one, but I can't comment at all on journals that use the new one because the "Post comment" button stays greyed out and unclickable.

How do some people get the comment box that works? Is it a paid-only option? I'd like to enable it on my LJ so I can reply to my own comments. And is there any work-around that will allow me to participate in comms that use the new style? I've had a dig around but can't find any option for it, so if it's something I can change within LJ, please find me a road map...

Edit: fixed by removing an obsolete Greasemonkey script. Thanks everyone!