But it's unlikely that Google would ditch the deal, said Al Hilwa, an analyst with IDC.

"These contracts are based on access to users who might be exposed to Google through the browser ... [and] Firefox still has a significant share that is worthwhile to pay for," said Hilwa. "I don't see the value for Google to abandon that crowd because doing so is not going to help Chrome gain any more traction."

According to a pair of Web analytics firms, as the second-most-used browser sometime between the end of this year and the middle of 2012.

U.S.-based Net Applications, for example, said of all browsers used in September was 16.2%, while Firefox's was 22.5%.

Mozilla also noted its 2011 revenues included some "very important individual and corporate donations."