Get the User Agent Switcher extension for firefox
here.
Install it.
Restart Firefox.
Using the User Agent extension, add a new agent called "Google".
Add this as the "user agent" string:
Googlebot/2.1 (+
http://www.googlebot.com/bot.html)
Now you can browse the internet and see what a Google bot will see. What will happen is that when you connect to a website, the website will think that you are a Google bot and allow you to access webpages that you may normally not be able to access. For example, you can by-pass annoying ads and the free registration processes that some sites make you go through to connect.
AFAIK it's perfectly legal to do this, although some may say it's unethical. Use your better judgment, and if you want you can always click on the ads or register.