Mozilla, the open source organisation responsible for Firefox, joined other major technology companies today to protest anti-piracy legislation by blackening the browser's home page.

Firefox's default home page, essentially a search field for Google, will change from its usual white background with the Firefox logo to a blacked-out version displaying a modified graphic emblazoned with "Stop Censorship."

Meanwhile, the English language versions of Mozilla's sites, and, will redirect visitors to an "action page" asking for their support in stopping what it called "Internet blacklist legislation."

Mozilla and an estimated 7,000 other sites, including Google, Wikipedia and Reddit, went on a "virtual strike" today to voice their opposition to the Stop Online Piracy Act (SOPA) and the Protect IP Act (PIPA), legislation being considered by the US government.

Some of the sites went completely dark. Wikipedia blocked its English content, replacing it with an anti-SOPA/PIPA call to arms, but others like Mozilla used milder methods. Google, for example, placed a black rectangle over the area where it normally positions its logo or specialty "doodles".

Although SOPA and PIPA are designed to make it easier for US copyright holders to retaliate against foreign websites that distribute pirated movies, music and software, opponents have argued that if they are made law, the bills will give content owners enough leverage to censor domestic websites.

"These new laws would give the US government and private business incredible censorship powers that would have effects globally, damage the Internet's security and discourage innovation and investment worldwide," a Mozilla statement claimed.

Mozilla was one of nine companies that jointly signed a letter last November to key members of Congress, saying that SOPA and PIPA "pose a serious risk to our industry's continued track record of innovation and job-creation, as well as to our Nation's cybersecurity."

Approximately one-out-of-four Internet users rely on Firefox to access the Internet, according to statistics from metrics firm Net Applications.