Firefox Version is Different
In the comments of our thread on the Google Toolbar Pushing Autolink with an Autoupdate, Graywolf discovers that the Firefox version overwrites existing links!
Marissa Mayer said explicitly that this would not happen:
Hyperlinking their own content is the best way publishers can prevent Google from adding links to their pages, Mayer said, because Google's technology will not override existing links.
But, if you check out this page for example and hit "autolink" the addresses, that are already linked are completely overwritten by Google with links to their own content. If you don't have the toolbar on FF, or just can't be arsed to install it (and who'd blame you?) then see this screenshot of the overwritten links.