I have same problem. However, this problem occures only on Firefox 3.6.12 on Microsoft Windows. This problem does not occur on Firefox 3.6.12 on Mac OS X and FreeBSD.

Solved.

1. "about:config" 2. change "dom.storage.enabled" to "true" 3. reload

Please see: https://support.mozilla.com/en-US/questions/761734

I got the URL via this page. ( in Japanese ) http://akonno.blogspot.com/2010/11/firefox-3612-gmail.html

I had the same problem. I followed all the advice posted on various forums, but none of them worked. Now I have found a solution which has worked, and it may work for you if your circumstances are the same as mine. The problem was my 3Mobile broadband dongle. I discovered this when I used a BT O2 dongle and suddenly all Google applications started working again with Firefox. But when I switched back to the 3Mobile dongle they stopped working. This was strange because Google applications were working properly with 3Mobile dongle on IE8 and Google Chrome. The solution: I simply called 3Mobile technical support, and they helped me to adjust the settings in my dongle (advanced setting/connections/properties: and then I had to clear the existing address and type in three.co.uk). Problem solved. Although anyone reading this may not be with 3Mobile, I thought that I would post this note, just in case the problem is with your broadband connection.