After installing version 13 of Firefox, I found access to Google sites to be extremely slow. It turns out that Google has implemented a new protocol on its sites named SPDY (short for speedy) that is supposed to speed up the serving of web pages. Sadly, the Firefox implementation of this new protocol seems to be flawed. In order to fix the problem you need to turn off the SPDY protocol in Firefox.
To do this you need to enter about:config in the URL bar. Then find network.http.spdy.enabled and double click it to change its value to false. This disables SPDY in Firefox and speeds up access to Google.