How to get back to my email from a locked page ?

After reading my emails, I wanted to look at my address book. I clicked on ADDRESS BOOK and my book was not there. Now, I can't back up to a normal page. The only choice is to go to the taskbar and close that page. Then when I restart Thunderbird, I get the same useless page ! Now how do I get my emails ? PS I cannot get to the HELP page of Thunderbird in order to find the version number, so the number I posted below is probably wrong. But otherwise, I could not SUBMIT my plea for help. I'm really stuck !!