Granted, your mileage may vary based on your hardware, operating system, and other factors, but there's no denying the fact that Firefox 4 is much faster at handling JavaScript than Firefox 3.6.

New in Firefox 4 is Firefox Sync, which lets you sync your bookmarks, browsing history, passwords, and other data with your other computers running Firefox. (This was previously available via an extension called .).

To use Firefox Sync, go to the Options Pane (open the Firefox menu and click Options,) then select Sync from the toolbar. From there, you can create a new Firefox Sync account. Setting up an account is fairly easy--it'll ask you to enter your e-mail address and create a password--but things get a little more complicated after that.

Firefox will give you an alphanumeric "Sync Key" that you'll need to write down, save to your disk, or print to keep safe. You'll need this key to be able to access your Firefox Sync account on another PC or smartphone, and if you lose it, you're out of luck--it can't be recovered.