Thunderbird cannot receive new mails

I have setup Mozilla Thunderbird as my email client for my gmail account. I followed the instructions provided by gmail to setup Thunderbird. Both the setup and configuration was fine and when I connected to internet Thunderbird managed to get all my emails in its inbox. I sent an email from Thunderbird to my yahoo account, it was successful, however I sent a mail from yahoo to gmail and checked it if Thunderbird could receive it or not and unfortunately it could not receive it. I clicked the Get Mail button several times and waited for more than half an hour but nothing happens. Please help me
I have never used email clients before, it is just because I love Firefox that I tried Thunderbird. How can I password protect my account in Thunderbird and like the about:config magic in Firefox do we have anything like that to speed up Thunderbird