I asked Google this question a few weeks ago and this was their reply.
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Thank you for your note, and your kind words. We decided to first release the Google Toolbar for Microsoft Internet Explorer. We are examining the
feasibility of offering a toolbar that is compatible with other browsers such as Netscape and Mozilla Firefox; however, this version is currently unavailable. We apologize for this inconvenience and will keep your feedback in mind for future versions of the Toolbar.
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Friends Newsletter at
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Regards,
The Google Team
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imaginemn