Update: It's working for me now.
I don't know exactly what fixed it. I deleted the manually-installed script and disabled all add-ons except Greasemonkey. Then I installed the script again and loaded the reader page. Now the script works even with all add-ons re-enabled. My best guess is that some add-on or other was interfering with the installation process somehow.
I posted this script previously to Open Thread, but it got broken by the discussion/main split-up and also didn't work in Firefox 4. It's now updated and fixed for Firefox 4. The original description follows. See the previous thread for some additional questions and answers. (ETA: Firefox 4 seems to have made the script much faster, so try it again if you were previously put off by the slowness.)
For those who may be having trouble keeping up with "Recent Comments" or finding the interface a bit plain, I've written a Greasemonkey script to make it easier/prettier. Here is a screenshot.
Explanation of features:
To install, first get Greasemonkey, then click here. Once that's done, use this link to get to the reader interface.
I've placed the script is in the public domain. EDIT: Chrome is supported as of version 1.0.5 of the script.
On a related note, here is a way to view all posts and comments of a particular LW user as a single HTML page.
EDIT - Version History: