I encountered a strange issue the other day where a client couldn’t upload attachments to Gmail using Firefox. It worked fine in IE8 (Windows XP), and the rest of Gmail seemed to work, just attachments were weird. I disabled spdy in about:config and uploading suddenly worked flawlessly. In tracking down the issue, I noticed that she had the BSecure Cloud Care content filter installed. On a hunch, I used another laptop to test attachment uploading in Firefox (it worked fine), then installed BSecure and tried again. It failed the second time until I disabled spdy.
As a sidenote, once I added mail.google.com to the whitelist in Cloud Care on the second computer, uploading worked fine with spdy enabled. It already was in the whitelist on the first computer, so I’m not sure what is occurring there. My guess is that some other element was blocked at some point.
The workaround was to simply disable spdy on the first computer. Not a great solution given the benefits that spdy provides, but the best one for that situation.
I didn’t see any information regarding this issue on the internet, so I am posting this for posterity.