I wouldnt think so. Did you say your password with firefox or ie? If so someone could have grabbed the cookie. Or if you forget to sign off someone can get to your account sometimes( at least on hotmail i remember it happenenig ). I would say email google to at least address the problem and see what kind of advice they could give you on if theres a possibility to retrieve data.
Next time around take advantage of gmails option to use a POP3 server. I have it configured to work with outlook and it will save my emails to my computer locally.
HTH.
ALSO.. when using websites at a remote computer, always make sure remember me isnt checked. I made that mistake in class a couple times. Its crazy looking through students history and having complete access to forums, web based email sites, and online banking. Gotta be careful on public computers.