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.
My default browser is Mozilla Firefox and I've just downloaded the Google toolbar - but it doesn't display on my browser. It IS there on IE. How can I get it to display?