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Firefox Nightly features a new internal Web Compatibility page that lists Firefox compatibility modifications for Internet sites and services.

While it is usually in the best interest of webmasters and companies to make sure that their sites display and work fine in all popular web browsers, it sometimes is not the case.

Web developers may test a site only in Chrome, the dominating browser when it comes to marketshare, or implement functionality that is only supported by certain browsers.

Browser makers like Mozilla face a tough decision when they notice that certain sites or services don't work properly in their browsers. While they could ignore incompatible sites, especially if a site uses non-standard technologies, it would fall back to the browser if users of it could not access a site or use certain features.

Making sites compatible in the browser, on the other hand, might send the wrong signal. While that is better from a user perspective, more and more sites might ignore all but the most popular browsers.