Google Chrome has a great feature, incognito mode. Press Ctrl-Shift-N or select Wrench / New incognito window and you get a browser window with no state. No cookies, no cache, no browser history, no addons, nothing loaded before the page and nothing saved after. (Firefox, Safari, and IE can do this too).

This mode is half-jokingly called “porn mode”, but I find it very useful as a software developer. Some ways I use it:

• Testing links before sending them out. Check whether the link you’re about to send your friend gives them the same page you see or if the page requires a login or cookie to look as intended.
• Debugging Javascript. Chrome extensions confuse Javascript debugging; the scripts show up in the developer console and you never can be sure whether some addon is modifying things. Incognito mode loads no extensions unless you explicitly enable one.
• Bypassing caching. It’s hard to test a webapp reliably, particularly for performance, when so many of the assets in the page may be cached. A new incognito window starts with no cache. The window seems to keep a memory cache, so you can also test your caching behaviour after the initial clean load.

Porn mode was invented for browsers to not store state after ending a session. But I find I mostly use it to not load state before starting a session.