Sorry but it's not available on Mozzila YET. I'm copying and pasting this off the FAQ from Google.

Q.Does the toolbar work with Mozilla/ Netscape/ Linux/ Firefox/ AOL or MSN?

A.We decided to first release the Google Toolbar in Microsoft Internet Explorer. We are examining the feasibility of offering a toolbar that is compatible with other browsers such as Netscape and Mozilla; however, this version is currently unavailable. We apologize for this inconvenience and will keep this suggestion in mind for future versions of the Toolbar.