Googlebar has been updated to make it compatible with Firefox 1.5. It was possible to fool Firefox into allowing the earlier Googlebar extension to be installed by using the Nightly Tester Tools but one could not guarantee that all the buttons would work. Note that this is not the Toolbar provided by Google but a completely separate project. I much prefer the Mozdev Googlebar as it offers far more search options from the toolbar including video, book, Scholar, Maps, Local and Glossary search.