Recently I was faced problem while attaching document on gmail using firefox browser. I was followed the below steps to resolve the problem in my firefox v32.0.3 browser.
Step 1: In Firefox address bar, type “about:config”.
Step 2: Agree to warranty warning.
Step 3: In search area type “network.http.spdy”, It will list the filtered result in the page.
Step 4: Double click the “Network.http.spdy.enabled” so that the value becomes false.
Step 5: Now restart your firefox browser.
It will works, I worked for me on Windows7, Firefox and Kaspersky firewall. Feel free to share your comments to improve the post details.