First look to Mozilla Labs Weave

The door is open again and registration available for Weave, Mozilla Labs’ application for synchronizing Firefox metadata online.

To register, visit Weave User Registration site. You only need to provide a valid email address, a password, proof you’re human (thorugh a CAPTCHA test) and click the activation link you will receive by email.

On activation you will be prompted to install the Weave extension (press Allow in the information bar to authorize which is compatible for Firefox 3 Beta 2 and nightlies.