I noticed recently that, when replying to a thread in the forums, I had to take my eye one or two screens down the page in order to review the recent posts in the thread, and that other folks often responded to threads between the time that I began and posted my reply, causing my comments to sometimes be "behind" before I ever posted them. Also, I found it cumbersome that the forums only make it really easy for me to quote one person per reply.
These things remind me that I'm using a message board to communicate, as they depart from what I'd experience if I were talking with folks face to face. I've modified the reply composition page for myself by authoring a userscript for use in the Greasemonkey Firefox extension. Anyone may use it if he likes. I've called it, simply, Live Thread Review.
The userscript modifies, rather significantly, the page you see when you reply to a thread. In short, it moves a bit to the left the composition textfield, creating room on the right for the most noticeable addition: an automatically refreshing display of the thread's most recent replies. If someone replies to the thread while I'm composing my reply, I can easily see that and immediately include his comments in the composition I'm still creating. I'm reviewing the thread, live, while I reply to it.
By clicking on the name of the author, his name is inserted into my reply at the cursor location. By clicking on the author's comments, he is quoted in my reply, again at the cursor location.
livethreadreview.user.js
By design, this userscript causes no posts in the forums to be marked as read. So, yes, you'll have to later read (in New Posts, or whatever) posts which happen while you're composing your reply. I built it that way on purpose, as the last thing I want is for folks to overlook posts.
If you have any questions about how to install or use this, please do use Google to educate yourself minimally about Greasemonkey before asking questions.
Many thanks to Pokerface, who spent quite some time helping me make this even usable. If you do use this, please do provide feedback in this thread. I anticipate there's much room for improvement here. If you encounter a bug, screenshots would help me a lot with this one.