maijor,

According to Wikipedia's SPDY article, SPDY is an open networking protocol developed primarily at Google for transporting web content. It's enabled by default starting in Firefox 13. The goal of SPDY is to reduce page load time.

If you are using the latest version of Firefox and you are having problems with Google Mail or with other SPDY-enabled websites, changing "network.http.spdy.enabled" to "false" is a workaround until the problem can be resolved. If you need more help you should start your own thread as this one was started by bklyngrrl on June 21, 2012 and is almost 6 months old.

You can use this link as a starting point, to ask a new question: https://support.mozilla.org/questions/new

Are there any other network.http prefs that aren't the default (i.e. show as bold, user set) that may be causing this problem?