Opera has 100m active users worldwide.
Web browser Opera says that downloads of its software have doubled since Microsoft introduced browser choice to Windows users on 1 March.
Microsoft now offers customers a choice of 12 browsers rather than installing its own Internet Explorer browser as a default.
A screen offering users the chance to switch browser is rolling out across Europe as part of a Windows update.
Opera says that in Poland 77% of downloads have come from the screen.
The number of copies downloaded in Poland were up by 328% on normal levels in the three days Opera analysed, between 12 and 14 March.
The screen has also made a big impact on Opera downloads in Spain, Italy and Denmark where downloads have doubled and over 60% of traffic is coming from the screen.
"This confirms that when users are given a real choice on how they choose the browser, they will try out alternatives," said Hakon Wium Lie of Opera Software.
While the Norway-based company has focused on the European market, according to StatCounter GlobalStats in March 2010 Opera was the biggest browser in Russia with a market share of 32.76%, beating Internet Explorer, Firefox, Chrome and Safari.
Microsoft agreed to offer users browser choice in Europe as part of a settlement following a 10 year dispute with the European Commission over competition regulation.