Rated 5 out of 5 stars

To make Googlebar 0.9.20 work in Firefox 8:

1. Download the googlebar XPI
2. Open it with 7-Zip or another ZIP manager
3. Edit install.rdf and change the maxVersion value "8.*";
4. Save and let 7-Zip update the XPI
5. Drag and drop the file to Firefox
6. Restart Firefox
That's it.