Actually, SPDY protocol is enabled by default in all modern compatible browsers. Widely accepted browsers are SPDY compatible except Microsoft IE.
about:config at the URL address space and the following disclaimer will appear:
Press the procceed button and type in spdy at the search space.
The SPDY settings will appear. Please note that
network.http.spdy.enabled should be true, as well as the v2 and v3 parameters.
Now, to check the SPDY sessions, install Firebug addon on your Firefox
Goto Tools – Web Developer – Firebug – Open Firebug and open up the Gmail webpage. Checkout the Response Headers of the page looking for parameter X-Firefox-Spdy: 3. This ensures that SPDY protocol is used and indicates the negotiated version.
On chrome you can even watch the SPDY sessions by typing
chrome://net-internals on the URL and selecting the SPDY option on the left menu.
There is no official announcement from Microsoft yet, but Internet Explore 11 may support Google’s SPDY protocol.