Google has hired the head software engineer behind Mozilla's Firefox application, heightening speculation that the internet advertising company is planning to go head-to-head with Microsoft in the browser market.

Ben Goodger will join several engineers already hired by Google from Microsoft's dominant Internet Explorer (IE) software team.

Google, which has cultivated a reputation for being reluctant to comment on business developments, today refused to expand on Mr Goodger's role.

The company told Times Online: "Ben is a very talented engineer. His experience and skills match Google's interest in exploring interaction between browsers and services and products like Google Toolbar. We're very lucky to have him."

The company also downplayed suggestions that Mr Goodger had "defected", pointing out that though he would become a Google employee, Google would "donate" half his time back to the Mozilla Foundation, which is a non-profit software developer.

Mr Goodger's move could mark a step-change in the battle between Google and Microsoft, a rivaly that has escalated furiously since Google's flotation on the stock market last summer.

In recent months Microsoft launched its own internet search engine in a bid to topple Google's dominance in the lucrative paid-search advertising market. In turn, Google has entered - along with Yahoo, the world's most popular website - into desktop search software. The move by Google into products which help users find files on their PCs has been interpreted as the first stage of a serious challenge to Microsoft Windows, the phenomenally successful operating system.

Microsoft currently dominates the browser market, accounting for more than 90 per cent of users. But Firefox, Mozilla's "opensource" software alternative, which is available for free online, has shown signs of eroding the software giant's lead.

Such is the cultish popularity of Firefox, United States advocates of the browser raised $250,000 to take out a full page advert in the New York Times to announce its release. Its supporters claim that it is faster than IE and less prone to attack by internet viruses. The software has also won over fans by blocking annoying pop-up adverts.

The Firefox browser has been downloaded more than 20 million times to take between 5 and 8 per cent of the browser market, according to industry estimates. Experts have said that its popularity could explode if it were to be linked to Google's popular brand, which is highly visible online.

Moreover, experts have observed that there would be a certain symmetry if Mozilla were to mount a serious challenge to Microsoft - especially by way of free software. The open-source outfit traces its origins to the group of engineers that developed the Netscape browser which led the market before Microsoft released Internet Explorer, which rushed to prominence after it was given away with the Windows operating system included with most PCs sold - for free.

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