2012 error gmail manager Rated 5 out of 5 stars

In the past few days (since 2012 january 04-06) when I click on the gmail manager icon in FF9.0.1 to log in, sometimes it redirects me to the gmail login screen with captcha and I have to enter my password and also captcha.
But when I close firefox and restart it, everything is OK and I can log in to my gmail account without entering password as usual.

Does anyone know what's going on? Someone is trying to hack my account?

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