There is nothing you can do now. You can change you password to something else and take measures to make sure your email account is not hacked again. You can also visit the Gmail help pages for help. You can also try the following

Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

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By the way, spamming software can assign any "From" name and address that the spammer likes. In fact, they like to use names from the recipient's contact list to trick the recipient into trusting the message.

So just because someone received a message that claimed it was from you does not mean your account was compromised. You would need to have additional evidence, such as: everyone in your address book was spammed; messages in the Sent Items; lots of stuff deleted; password changed.

Still, good idea to change your password.

Definitely change password to something harder, and your security questions as well. It sucks to get hacked.

Good luck!

Thanks for the help!