It looks like the marriage between Google and Firefox is getting even stronger. Various independent sources have spotted a promotional ad smack in the middle of Google's homepage.

The promo can only be seen by U.S. users that browse with Internet Explorer, but this is still a huge coup for the upstart Mozilla browser because Google's homepage is essentially the most valuable piece of advertising space on the internet today.

However, this isn't exactly "free" advertising. Remember that Google's search bar is included as part of the Firefox browser package (and Google makes money every time someone clicks on one of their sponsored ads with search) so its in Google's best interests to promote this rather new but surprisingly versatile browser. And of course, let us not forget that Firefox is fast becoming the onlylegitimate competitor against Microsoft's IE.

So all and all its a pretty smart move for the folks over at Google. Every new Firefox subscriber equals more ad revenue for big "G" and another small axe striking at the big tree that is Microsoft.