According to Weblogs Inc founder Jason Calacanis, Firefox made $72m (about £41m) last year – or at least that's what someone told him.

How does a browser that's given away for free make so much money? It's all to do with the Google search box, apparently.

Enter a search using the box at the top right, rather than at Google.com directly, and Firefox gets a share of any revenue created as a result of Google Ads generated by that search – as much as 80 percent.

Christopher Blizzard, who's on the board of the Mozilla Corporation – makers of Firefox – says the $72m figure is "not correct, though not off by an order of magnitude".

Not a bad little earner, really.