Google has made "Extensions" to Firefox browser. One in particulary peaked my interest: Web Comments.
When installed to your Firefox, it shows blog comments that have been made about the page you are currently viewing. For example, stay in touch what people write about your blog, or your personal homepage! Über cool.
Other extensions made by Google:
Update 21.9.2013: Please note that this was 2007. Google Toolbar for Firefox has been discontinued, Blogger Web Comments for Firefox has been discontinued, the follow-up Google Sidewiki has been discontinued as well.