Microsoft’s failure to follow through with a 2009 agreement with the European Commission to provide Windows users in that region with a browser choice ballot box in Windows 7 has been well documented. Up to this point, the commission has been the only one to field complaints but now we’re hearing that at least one competing browser provider may have suffered thanks to Microsoft’s blunder.

In a recent post on his blog, Mozilla’s Harvey Anderson said Firefox downloads decreased by 63 percent to a low as 20,000 just before Microsoft fixed the problem. He says that after Redmond put the browser ballot box back in place, daily downloads of Mozilla’s web browser jumped 150 percent to 50,000 per day.

Cumulatively, Mozilla believes that roughly six to nine million downloads were lost during the almost 15 month period where the ballot box was missing. We haven’t heard anything from other browser makers like Apple, Google or Opera but one would have to image that their download rates would have tumbled as well during the same time.

Redmond ultimately claimed a glitch in Service Pack 1 prevented some 28 million PCs from displaying the dialog box. The European Commission has since filed a formal complaint against Microsoft. If found guilty of wrongdoing, they could face a fine to the tune of $7.3 billion.

My only question is that if Mozilla noticed such a huge drop in browser downloads (and assuming others did as well), why didn’t anyone look into it to discover that traffic had stopped coming from Microsoft’s ballot system? Surely there’s traffic data that would show an overnight loss of traffic from this source.