Mozilla and Google on Monday took steps toward giving people more online privacy but each said hurdles remain to creating simple "Do Not Track" buttons for Web browsing software.

Mozilla proposed adding a signal to its popular Firefox browser to let users automatically ask websites not to track their online activities.

Websites would then decide whether to grant the desire or continue to gather data for purposes such as targeting Internet advertising.

Firefox users would be able to broadcast that they want to opt out of third party, advertising-based tracking by setting browsers to transmit a "Do Not Track HTTP header" with every click or page view.

"The challenge with adding this to the header is that it requires both browsers and sites to implement it to be fully effective," Mozilla technology and privacy officer Alex Fowler acknowledged in a blog post.

"Mozilla recognizes the chicken and egg problem and we are taking the step of proposing that this feature be considered for upcoming releases of Firefox."

Google on Monday released extension software for its Chrome browser that lets users opt out of being tracked by a growing set of companies adopting industry privacy standards regarding online advertising.

"Keep My Opt-Outs" lets people opt out of having snippets of code referred to as "cookies" installed on their computers to track online behavior for the purpose of targeting ads.

"Keep in mind that once you install the Keep My Opt-Outs extension, your experience of online ads may change," Google product managers Sean Harvey and Rajas Moonka said in a blog post.

"You may see the same ads repeatedly on particular websites, or see ads that are less relevant to you."

The top 15 largest US ad networks are among the more than 50 companies involved in the opt-out program. Google is among the firms that also provide an option for people to specify what types of ads they are most interested in.

"Importantly, we've designed the extension so that it should not otherwise interfere with your Web browsing experience or website functionality," Harvey and Moonka said.

"This new feature gives you significant control without compromising the revenue that fuels the Web content that we all consume every day."

California-based Google said it is working to make the feature available to Web browsers other than Chrome.

Microsoft plans to increase privacy options in the upcoming version of its popular Web browser Internet Explorer 9 (IE9), including the ability to prevent tracking by third-party websites.

The US software giant said that the new feature, "Tracking Protection," is designed to "help consumers be in control of potential online tracking as they move around the Web."

The tool will be built into a test version of IE9 being released this year.

IE9 users will have to be savvy enough to create lists of third-party websites that they do not want to track their behavior.

Talk of Web browser privacy enhancements comes amid moves in Washington to create "Do Not Track" mechanisms in browsers to stop online services from collecting Web surfing or ad-targeting data.

Internet Explorer is the most widely used Web browser in the United States followed by Mozilla's Firefox, Google's Chrome and Apple's Safari.

"Technology that supports something like a 'Do Not Track' button is needed," Mozilla chief executive Gary Kovacs told AFP during a recent visit to Mozilla's headquarters in Mountain View, California. "The user needs to be in control."

Firefox debuted in 2004 as an innovative, communally crafted open-source browser released as an option to Internet Explorer.