An indicator in the address bar for SPDY usage by each website.
Server support and usage
As of March 2012, there are not many SPDY-enabled websites. Some Google services (e.g. Google search, Gmail, and other SSL-enabled services) use SPDY when available. Google's ads are also served from SPDY-enabled servers.
Twitter has enabled SPDY on its servers in March 2012, making it the second largest site known to deploy SPDY.
Cloudflare is also providing a beta of SPDY on their servers from June 2012, though users who would like to use/test it must be paying customers as SPDY is built on top of TLS, only paying customers can use SSL/TLS Certificates.
In March 2012, the open source Jetty Web Server announced support for SPDY in version 7.6.2, while other open source projects were working on implementing support for SPDY, like node.js, Apache (mod_spdy), curl, and nginx.
In April 2012 Google started providing SPDY packages for Apache servers which led some smaller websites to provide SPDY support.
In May 2012 F5 Networks announced support for SPDY in its BIG-IP application delivery controllers.
In June 2012 NGINX, Inc. announced support for SPDY in the open source web server Nginx.
In July 2012 Facebook announced implementation plans for SPDY.
In August 2012 Wordpress.com announced support for SPDY across all their hosted blogs.
For Firefox one can do this..but there is no reason to..be more concerned about TLS.