ExtremeTech has an article about the extensions they like to use for Firefox. The article covers:

  1. Adblock
  2. Image Zoom
  3. FoxyTunes
  4. easyGestures
  5. Gmail Notifier
  6. Image-Show-Hide
  7. Web Developer
  8. fireFTP
  9. WebmailCompose
  10. Homeland Security Threat Level

I use a couple of those and they make Firefox that much more enjoyable. Of course Firefox was much more enjoyable before I even touched those extensions.