Setting up a second device (PC, smartphone, etc...) to work with Firefox Sync also requires you to jump through some security hoops as well. For example, if you've already set up a Sync account and you want to set up Firefox Sync on your laptop so it stays in sync with what you have on your desktop, you'll need to go back to your desktop and enter in an authentication code.

If you don't have access to your desktop PC at the moment--say it's at home and you're traveling with your laptop--you'll need to enter the aforementioned Sync Key. If you left your Sync Key at home, you can't access your account. This sort of two-factor authentication is a bit of a double-edged sword; it's more secure than a password alone, but it can be a hassle.

Once you get Sync all set up though, it's easy to use. Everything is handled automatically and in the background, so you won't have to manually re-sync periodically.

Firefox 4 is a must-have upgrade if you're running Firefox 3.x. If you've switched from Firefox to Chrome, however, Firefox 4 may not offer quite enough to lure you back, as many of the new features--at least on the user interface end--are clearly influenced by Chrome. But no matter what, it may be and taking for a spin.