I can post, reply, "like", etc with all comments threaded - just fantastic. Unfortunately the developer, sandosh, decided a few months back to stop supporting the project. Once Firefox 3.0.x came out, the application wouldn't work out of the box anymore. (To resolve the 3.0.x issue, I set the option "extensions.checkCompatibility" to false as documented here.)
Recently, Friendfeed made a change to their API, requiring all API POSTs to use the friendfeed.com domain and rejected (with an HTTP 405 response code) any POST using the IP address of friendfeed.com. I opened up a bug with Friendfeed and supplied a netmon trace of a sample "like" POST. Gary Burd jumped on it and quickly figured out the problem.
As sandosh is no longer working on the project, I took a crack at making this change as follows:
1. Grab mysocial24x7.jar from <yourFirefoxProfile>/extensions/ffbar@sandosh/chrome
2. Unzip, edit ffbar.js, search/replace "184.108.40.206" with "friendfeed.com".
3. Update the jar with this file (zip -u mysocial24x7.jar content/scripts/*)
4. Restart Firefox.
You can also grab the modified .jar here
I noticed that the Twitter login functionality is now broken as well. Let me know if there is a fix out there for this.