I haven't run across Target Alert, but I'll definately check it out.

I currently use 4 extensions:

  • Tabbrowser Preferences: Enhances control over some aspects of tabbed browsing.
  • PDF Download: Allows one to choose whether one wants to view a PDF file inside the browser or in a separate window.
  • IE View: Opens pages in IE via Firefox menus
  • Web Developer: Adds a toolbar with various web developer tools (this one is a must have for web designers).