Gmail login claims cookies are disabled.
The gmail login page is sometimes claiming that cookies are disabled even when they are not.
This issue is caused by the hidden setting: extensions.torbutton.xfer_google_cookies.
This setting was introduced to reduce the number of captchas that google presented, so that you would only have to solve a captcha once, instead of once per country code domain.
We need to investigate exactly why this cookie transfer is now breaking the login process. Something must have changed with the cookie names/origins/etc.