Why is this so cool?
Weave lets you securely synchronize parts of your browser profile between different machines. All your bookmarks, AwesomeBar history, saved passwords can be synchronized between your laptop, desktop and mobile phone. Your data is always encrypted with a private key that only you have access to.
Combine this with intelligent form-filling, automatic detection of OpenID-enabled sites, and you've got what is essentially single sign-on onto all your websites from all your browsers.
Now you'll be able to sign into Firefox, and Firefox will know how to sign into all your websites.
Keep up the great work Labs!