For quite some time, Google hasn't updated the toolbar for Firefox 5, it turns out that Google no longer wants to update Google Toolbar for Firefox, but it doesn't admit that the product has been discontinued.
"Google Toolbar for Firefox is compatible with Firefox version 4 or older. If you use Firefox version 5 or newer, you won't be able to use Google Toolbar."
A Google blog post offers an explanation:
"First of all, we'd like to thank all of our loyal users of Google Toolbar for Firefox. We deeply appreciate all of the feedback over the years that helped to make the product so useful. As we all know, over the past few years, there has been a tremendous amount of innovation in the browser space". For Firefox users, "many features that were once offered by Google Toolbar for Firefox are now already built right into the browswer. Therefore, while Google Toolbar for Firefox works on versions up to and including Firefox 4 only, it will not be supported on Firefox 5 and future versions. Please see our Help Center for additional details.."
That's also true for the IE toolbar, but there are many useful features that aren't included in the browser: auto-translation (a built-in Chrome feature), Google Bookmarks integration, using Google Docs to open documents, smart spell-checking using an online service, highlighting search terms, suggestions for navigation errors (another built-in Chrome feature), custom buttons and gadgets.
For now, Google Toolbar still works in the latest Firefox releases if you install the Add-on Compatibility Reporter first and restart the browser.
Here's Google Toolbar in Firefox 7 Alpha 2 (Aurora):
[Source: Google Toolbar Help, Thanks, Alex]