Secure Sockets Layer (SSL) is a security protocol that requires a web server and browser to work together to establish an encrypted channel for the exchange of information. Seamless trust between a browser and server depends on the browser's ability to trust the SSL provider.
Browsers determine whether or not to trust an SSL certificate by checking the source of the certificate issuance. If the SSL certificate is issued by a Certificate Authority that is known and trusted by the browser, the browser extends that trust to the web site secured by the SSL certificate. If the certificate is self-signed or issued by an unknown Certificate Authority, the browser may display an alert or security warning.
Most browser vendors release their software with pre-installed root certificates from known Certificate Authorities. An SSL certificate's root ubiquity or level of browser recognition (also called browser compatibility) reflects the number of browsers that trust the Certificate Authority. There may be a few older or uncommon browsers missing root certificates. This is why SSL providers do not claim 100% browser compatibility.
RapidSSL Certificates are recognized by more than 99+% of browsers.