Earlier this week, Google announced it was killing Google Toolbar for Firefox, and would not be updating the add-on to support Firefox 5 or future versions of the open-source browser.
Google seems to have taken everyone by surprise by this move (http://www.pcworld.com/article/236418/mozilla_hustles_to_handle_demise_of_google_toolbar_for_firefox.html). While I am not screaming in horror like some people (http://googletoolbarhelp.blogspot.com/2011/07/update-on-google-toolbar-for-firefox.html), I did find it to be a useful addition and it will be missed.