Every web browser has varying levels of support for fonts linked via @font-face. Web Font Loader determines support for web fonts is using the browser's user agent string. The user agent string may claim to support a web font format when it in fact does not. This is especially noticeable on mobile browsers with a "Desktop" mode, which usually identify as Chrome on Linux. In this case a web font provider may decide to send WOFF fonts to the device because the real desktop Chrome supports it, while the mobile browser does not. The Web Font Loader is not designed to handle these cases and it defaults to believing what's in the user agent string. Web font providers can build on top of the basic Web Font Loader functionality to handle these special cases individually.