Look at the “Project releases” links on the main OpenNTF project page, click the latest release, and follow the install instructions on that page.
What this script does is add a little [+] next to each response link at the bottom of a message that you’re looking at. If you click the [+] next to a response, the text of the response will appear below the link, so you can read it inline instead of having to open a new window.
This will work for all the responses to a thread, so you can read all the responses to a message inline, on a single page.
If you find any bugs or have any suggestions for improvement, please use the OpenNTF project discussion forums (since I don’t want to have to keep checking back here to see if people have questions).